🕷️ Crawler Inspector

URL Lookup

Direct Parameter Lookup

Raw Queries and Responses

1. Shard Calculation

Query:

Response:

Calculated Shard: 43 (from laksa096)

2. Crawled Status Check

Query:

curl -X POST \
  'http://laksa043.int.ahrefs:8124/' \
  -H 'Content-Type: text/plain' \
  -H 'X-ClickHouse-Database: crawler3' \
  -H 'Authorization: Basic YXBpOg==' \
  -d 'SELECT getAhrefsURLFromUnparsed(src_unparsed) AS found_url, ifNull(toUnixTimestamp(download_stamp), 0) AS crawl_time, ifNull(toUnixTimestamp(props_url_first_seen), 0) AS first_indexed_time, download_http_code AS http_code, src_unparsed AS src_unparsed, src_root_hash AS src_root_hash, history_drop_reason AS history_drop_reason, meta_title AS meta_title, meta_descriptions AS meta_descriptions, attrs_boilerpipe_text AS attrs_boilerpipe_text, attrs_markdown AS attrs_markdown, attrs_readable_markdown AS attrs_readable_markdown, meta_canonical AS meta_canonical, ml_categories_json AS ml_categories_json, ml_types_json AS ml_types_json, ml_intent_types_json AS ml_intent_types_json, meta_language AS meta_language, attrs_author AS attrs_author, ifNull(toUnixTimestamp(attrs_publish_time), 0) AS attrs_publish_time, ifNull(toUnixTimestamp(attrs_original_publish_time), 0) AS attrs_original_publish_time, ifNull(attrs_is_republished, 0) AS attrs_is_republished, ifNull(attrs_nr_words, 0) AS attrs_nr_words, ifNull(attrs_boilerpipe_nr_words, 0) AS attrs_boilerpipe_nr_words, ifNull(body_ext_links_number, 0) AS body_ext_links_number, ifNull(body_int_links_number, 0) AS body_int_links_number, ifNull(meta_nofollow, 0) AS meta_nofollow, ifNull(meta_noarchive, 0) AS meta_noarchive, ifNull(props_was_rendered, 0) AS props_was_rendered, ifNull(src_redirect, \'\') AS src_redirect, ifNull(download_time_msec, 0) AS download_time_msec, ifNull(download_ttfb_msec, 0) AS download_ttfb_msec, ifNull(download_size, 0) AS download_size FROM crawler3.page_info_local FINAL PREWHERE (src_root_hash, src_unparsed) IN ((getAhrefsRootHashFromUnparsed(getAhrefsUnparsedNoserviceFromURL(\'https://quickmathintuitions.org/why-hash-tables-should-use-prime-number-size/\')), getAhrefsUnparsedNoserviceFromURL(\'https://quickmathintuitions.org/why-hash-tables-should-use-prime-number-size/\'))) FORMAT JSONEachRow'

Response:

{"found_url":"https:\/\/quickmathintuitions.org\/why-hash-tables-should-use-prime-number-size\/","crawl_time":1776157901,"first_indexed_time":1555693603,"http_code":200,"src_unparsed":"org,quickmathintuitions!\/why-hash-tables-should-use-prime-number-size\/ s443","src_root_hash":"18237700010392947643","history_drop_reason":null,"meta_title":"Why hash tables should use a prime-number size — Quick Math Intuitions","meta_descriptions":["Why should hash tables have a prime number for its size? The best size for a hash table has to do with the fact that computers handle data in binary form."],"attrs_boilerpipe_text":"I read in several books and online pages that hash tables should use a prime number for the size. Nobody really justified this statement properly. Here’s my attempt!\nI believe that it just has to do with the fact that computers work with in base 2. Just think at how the same thing works for base 10:\n8 % 10 = 8\n18 % 10 = 8\n87865378 % 10 = 8\n2387762348 % 10 = 8\nIt doesn’t matter what the number is: as long as it ends with 8, its modulo 10 will be 8. You could pick a huge power of 10 as modulo operator, such as 10^k (with k > 10, let’s say), but\nyou would need a huge table to store the values\nthe hash function is still pretty stupid: it just trims the number retaining only the first\nk\ndigits starting from the right.\nHowever, if you pick a different number as modulo operator, such as 12, then things are different:\n8 % 12 = 8\n18 % 12 = 6\n87865378 % 12 = 10\n2387762348 % 12 = 8\nWe still have a collision, but the pattern becomes more complicated, and the collision is just due to the fact that 12 is still a small number.\nPicking a big enough, non-power-of-two number will make sure the hash function really is a function of all the input bits, rather than a subset of them.\nFor example, with 367:\n8 % 367 = 8\n18 % 367 = 18\n87865378 % 367 = 73\n2387762348 % 367 = 240\nWhat is worth nothing is that there may be a pattern even with modulo 367, but it would be way less trivial than with modulo 10 (or with modulo 2 in binary).\nWe don’t really need a prime number\n, just having a big non-power of two is enough. Having a prime number, obviously, is just a guaranteed way of satisfying those conditions.\nWas this Helpful ?\nyes\n   \nno\nPost navigation","attrs_markdown":"[Skip to content](https:\/\/quickmathintuitions.org\/why-hash-tables-should-use-prime-number-size\/#primary)\n\n[Quick Math Intuitions](https:\/\/quickmathintuitions.org\/)\n\nSharing quick intuitions for math ideas\n\n[Computer science](https:\/\/quickmathintuitions.org\/category\/computer-science\/)\n\n# Why hash tables should use a prime-number size\n[Stefano Ottolenghi](https:\/\/quickmathintuitions.org\/author\/qmi\/)\n\n[2017-06-012018-03-12](https:\/\/quickmathintuitions.org\/why-hash-tables-should-use-prime-number-size\/)\n\n[0](https:\/\/quickmathintuitions.org\/why-hash-tables-should-use-prime-number-size\/#respond)\n\nI read in several books and online pages that hash tables should use a prime number for the size. Nobody really justified this statement properly. Here’s my attempt\\!\n***\nI believe that it just has to do with the fact that computers work with in base 2. Just think at how the same thing works for base 10:\n\n- 8 % 10 = 8\n- 18 % 10 = 8\n- 87865378 % 10 = 8\n- 2387762348 % 10 = 8\n\nIt doesn’t matter what the number is: as long as it ends with 8, its modulo 10 will be 8. You could pick a huge power of 10 as modulo operator, such as 10^k (with k \\> 10, let’s say), but\n\n1. you would need a huge table to store the values\n2. the hash function is still pretty stupid: it just trims the number retaining only the first *k* digits starting from the right.\n\nHowever, if you pick a different number as modulo operator, such as 12, then things are different:\n\n- 8 % 12 = 8\n- 18 % 12 = 6\n- 87865378 % 12 = 10\n- 2387762348 % 12 = 8\n\nWe still have a collision, but the pattern becomes more complicated, and the collision is just due to the fact that 12 is still a small number.\n\n**Picking a big enough, non-power-of-two number will make sure the hash function really is a function of all the input bits, rather than a subset of them.**\n\nFor example, with 367:\n\n- 8 % 367 = 8\n- 18 % 367 = 18\n- 87865378 % 367 = 73\n- 2387762348 % 367 = 240\n\nWhat is worth nothing is that there may be a pattern even with modulo 367, but it would be way less trivial than with modulo 10 (or with modulo 2 in binary). **We don’t really need a prime number**, just having a big non-power of two is enough. Having a prime number, obviously, is just a guaranteed way of satisfying those conditions.\n\n- Was this Helpful ?\n- [yes](https:\/\/quickmathintuitions.org\/why-hash-tables-should-use-prime-number-size\/) [no](https:\/\/quickmathintuitions.org\/why-hash-tables-should-use-prime-number-size\/)\n\n[hash tables](https:\/\/quickmathintuitions.org\/tag\/hash-tables\/)\n\n## Post navigation\n[Metaphysics on geometric distribution in probability theory](https:\/\/quickmathintuitions.org\/metaphysics-on-geometric-distribution-probability-theory\/)\n\n[On the meaning of hypothesis and p-value in statistical hypothesis testing](https:\/\/quickmathintuitions.org\/meaning-hypothesis-p-value-statistical-hypothesis-testing\/)\n### Leave a Reply [Cancel reply](https:\/\/quickmathintuitions.org\/why-hash-tables-should-use-prime-number-size\/#respond)\n\n![Intuition image](https:\/\/quickmathintuitions.org\/wp-content\/uploads\/2016\/06\/My-aha-moments_float-e1466919792783.jpg)\n\n#### Categories\n- [Algebra](https:\/\/quickmathintuitions.org\/category\/algebra\/)\n- [Analysis](https:\/\/quickmathintuitions.org\/category\/analysis\/)\n- [Computer science](https:\/\/quickmathintuitions.org\/category\/computer-science\/)\n- [Cryptography](https:\/\/quickmathintuitions.org\/category\/cryptography\/)\n- [Finite Element Methods](https:\/\/quickmathintuitions.org\/category\/finite-element-methods\/)\n- [Graph theory](https:\/\/quickmathintuitions.org\/category\/graph-theory\/)\n- [Linear algebra](https:\/\/quickmathintuitions.org\/category\/linear-algebra\/)\n- [Meta](https:\/\/quickmathintuitions.org\/category\/meta\/)\n- [Modeling](https:\/\/quickmathintuitions.org\/category\/modeling\/)\n- [Numerical Analysis](https:\/\/quickmathintuitions.org\/category\/numerical-analysis\/)\n- [Probability](https:\/\/quickmathintuitions.org\/category\/probability\/)\n- [Statistics](https:\/\/quickmathintuitions.org\/category\/statistics\/)\n- [Uncategorized](https:\/\/quickmathintuitions.org\/category\/uncategorized\/)\n\n#### [![RSS](https:\/\/quickmathintuitions.org\/wp-includes\/images\/rss.png)](https:\/\/www.thecrowned.org\/feeds\/all-en.atom.xml) [Blog entries](https:\/\/thecrowned.org\/)\n- [On Karpathy's \"Software is changing (again)\"](https:\/\/thecrowned.org\/karpathy-software-is-changing)\n- [How many hours does it take to be pissed at France?](https:\/\/thecrowned.org\/france-joke)\n- [\"I'm really concerned about Hawai indigenous people's rights\"](https:\/\/thecrowned.org\/philosophy-of-science-class)\n- [Don't hurt pomegranates](https:\/\/thecrowned.org\/pomegranate)\n- [What love tells me](https:\/\/thecrowned.org\/mahler-love)\n- [The digital supermarket of human solitude (dating apps)](https:\/\/thecrowned.org\/dating-apps)\n- [How Feldenkrais made me the best math teacher](https:\/\/thecrowned.org\/feldenkrais-math)\n- [A cybersecurity take on the Swedish postal system](https:\/\/thecrowned.org\/postnord-drama)\n- [The dread of teaching pointless math ruins generations](https:\/\/thecrowned.org\/pointless-math)\n- [The differences between junior and senior software engineers](https:\/\/thecrowned.org\/junior-vs-senior-engineers)\n\nCopyright © 2026 [Quick Math Intuitions](https:\/\/quickmathintuitions.org\/ \"Quick Math Intuitions\").\n\n[Proudly powered by WordPress](https:\/\/wordpress.org\/)   \\|  Theme: Apace by [ThemezHut](https:\/\/themezhut.com\/themes\/apace\/).","attrs_readable_markdown":"I read in several books and online pages that hash tables should use a prime number for the size. Nobody really justified this statement properly. Here’s my attempt\\!\n***\nI believe that it just has to do with the fact that computers work with in base 2. Just think at how the same thing works for base 10:\n\n- 8 % 10 = 8\n- 18 % 10 = 8\n- 87865378 % 10 = 8\n- 2387762348 % 10 = 8\n\nIt doesn’t matter what the number is: as long as it ends with 8, its modulo 10 will be 8. You could pick a huge power of 10 as modulo operator, such as 10^k (with k \\> 10, let’s say), but\n\n1. you would need a huge table to store the values\n2. the hash function is still pretty stupid: it just trims the number retaining only the first *k* digits starting from the right.\n\nHowever, if you pick a different number as modulo operator, such as 12, then things are different:\n\n- 8 % 12 = 8\n- 18 % 12 = 6\n- 87865378 % 12 = 10\n- 2387762348 % 12 = 8\n\nWe still have a collision, but the pattern becomes more complicated, and the collision is just due to the fact that 12 is still a small number.\n\n**Picking a big enough, non-power-of-two number will make sure the hash function really is a function of all the input bits, rather than a subset of them.**\n\nFor example, with 367:\n\n- 8 % 367 = 8\n- 18 % 367 = 18\n- 87865378 % 367 = 73\n- 2387762348 % 367 = 240\n\nWhat is worth nothing is that there may be a pattern even with modulo 367, but it would be way less trivial than with modulo 10 (or with modulo 2 in binary). **We don’t really need a prime number**, just having a big non-power of two is enough. Having a prime number, obviously, is just a guaranteed way of satisfying those conditions.\n\n- Was this Helpful ?\n- [yes](https:\/\/quickmathintuitions.org\/why-hash-tables-should-use-prime-number-size\/) [no](https:\/\/quickmathintuitions.org\/why-hash-tables-should-use-prime-number-size\/)\n## Post navigation","meta_canonical":null,"ml_categories_json":"{\"\/Computers_and_Electronics\":961,\"\/Computers_and_Electronics\/Programming\":792}","ml_types_json":"{\"\/Article\":999,\"\/Article\/Tutorial_or_Guide\":814}","ml_intent_types_json":"{\"Informational\":999}","meta_language":"en-us","attrs_author":"Stefano Ottolenghi","attrs_publish_time":1496307456,"attrs_original_publish_time":1496307456,"attrs_is_republished":0,"attrs_nr_words":"549","attrs_boilerpipe_nr_words":"336","body_ext_links_number":14,"body_int_links_number":23,"meta_nofollow":0,"meta_noarchive":0,"props_was_rendered":0,"src_redirect":"","download_time_msec":1564,"download_ttfb_msec":1564,"download_size":12137}

3. Robots.txt Check

Query:

Response:

4. Spam/Ban Check

Query:

Response:

5. Seen Status Check

ℹ️ Skipped - page is already crawled

📄

INDEXABLE

✅

CRAWLED

11 days ago

🤖

ROBOTS ALLOWED

Page Info Filters

Filter	Status	Condition	Details
HTTP status	PASS	`download_http_code = 200`	HTTP 200
Age cutoff	PASS	`download_stamp > now() - 6 MONTH`	0.4 months ago
History drop	PASS	`isNull(history_drop_reason)`	No drop reason
Spam/ban	PASS	`fh_dont_index != 1 AND ml_spam_score = 0`	ml_spam_score=0
Canonical	PASS	`meta_canonical IS NULL OR = '' OR = src_unparsed`	Not set

Page Details

Property

Value

URL

https://quickmathintuitions.org/why-hash-tables-should-use-prime-number-size/

Last Crawled

2026-04-14 09:11:41 (11 days ago)

First Indexed

2019-04-19 17:06:43 (7 years ago)

HTTP Status Code

200

Content

Meta Title

Why hash tables should use a prime-number size — Quick Math Intuitions

Meta Description

Why should hash tables have a prime number for its size? The best size for a hash table has to do with the fact that computers handle data in binary form.

Meta Canonical

null

Boilerpipe Text

I read in several books and online pages that hash tables should use a prime number for the size. Nobody really justified this statement properly. Here’s my attempt! I believe that it just has to do with the fact that computers work with in base 2. Just think at how the same thing works for base 10: 8 % 10 = 8 18 % 10 = 8 87865378 % 10 = 8 2387762348 % 10 = 8 It doesn’t matter what the number is: as long as it ends with 8, its modulo 10 will be 8. You could pick a huge power of 10 as modulo operator, such as 10^k (with k > 10, let’s say), but you would need a huge table to store the values the hash function is still pretty stupid: it just trims the number retaining only the first k digits starting from the right. However, if you pick a different number as modulo operator, such as 12, then things are different: 8 % 12 = 8 18 % 12 = 6 87865378 % 12 = 10 2387762348 % 12 = 8 We still have a collision, but the pattern becomes more complicated, and the collision is just due to the fact that 12 is still a small number. Picking a big enough, non-power-of-two number will make sure the hash function really is a function of all the input bits, rather than a subset of them. For example, with 367: 8 % 367 = 8 18 % 367 = 18 87865378 % 367 = 73 2387762348 % 367 = 240 What is worth nothing is that there may be a pattern even with modulo 367, but it would be way less trivial than with modulo 10 (or with modulo 2 in binary). We don’t really need a prime number , just having a big non-power of two is enough. Having a prime number, obviously, is just a guaranteed way of satisfying those conditions. Was this Helpful ? yes no Post navigation

Markdown

[Skip to content](https://quickmathintuitions.org/why-hash-tables-should-use-prime-number-size/#primary) [Quick Math Intuitions](https://quickmathintuitions.org/) Sharing quick intuitions for math ideas [Computer science](https://quickmathintuitions.org/category/computer-science/) # Why hash tables should use a prime-number size [Stefano Ottolenghi](https://quickmathintuitions.org/author/qmi/) [2017-06-012018-03-12](https://quickmathintuitions.org/why-hash-tables-should-use-prime-number-size/) [0](https://quickmathintuitions.org/why-hash-tables-should-use-prime-number-size/#respond) I read in several books and online pages that hash tables should use a prime number for the size. Nobody really justified this statement properly. Here’s my attempt\! *** I believe that it just has to do with the fact that computers work with in base 2. Just think at how the same thing works for base 10: - 8 % 10 = 8 - 18 % 10 = 8 - 87865378 % 10 = 8 - 2387762348 % 10 = 8 It doesn’t matter what the number is: as long as it ends with 8, its modulo 10 will be 8. You could pick a huge power of 10 as modulo operator, such as 10^k (with k \> 10, let’s say), but 1. you would need a huge table to store the values 2. the hash function is still pretty stupid: it just trims the number retaining only the first *k* digits starting from the right. However, if you pick a different number as modulo operator, such as 12, then things are different: - 8 % 12 = 8 - 18 % 12 = 6 - 87865378 % 12 = 10 - 2387762348 % 12 = 8 We still have a collision, but the pattern becomes more complicated, and the collision is just due to the fact that 12 is still a small number. **Picking a big enough, non-power-of-two number will make sure the hash function really is a function of all the input bits, rather than a subset of them.** For example, with 367: - 8 % 367 = 8 - 18 % 367 = 18 - 87865378 % 367 = 73 - 2387762348 % 367 = 240 What is worth nothing is that there may be a pattern even with modulo 367, but it would be way less trivial than with modulo 10 (or with modulo 2 in binary). **We don’t really need a prime number**, just having a big non-power of two is enough. Having a prime number, obviously, is just a guaranteed way of satisfying those conditions. - Was this Helpful ? - [yes](https://quickmathintuitions.org/why-hash-tables-should-use-prime-number-size/) [no](https://quickmathintuitions.org/why-hash-tables-should-use-prime-number-size/) [hash tables](https://quickmathintuitions.org/tag/hash-tables/) ## Post navigation [Metaphysics on geometric distribution in probability theory](https://quickmathintuitions.org/metaphysics-on-geometric-distribution-probability-theory/) [On the meaning of hypothesis and p-value in statistical hypothesis testing](https://quickmathintuitions.org/meaning-hypothesis-p-value-statistical-hypothesis-testing/) ### Leave a Reply [Cancel reply](https://quickmathintuitions.org/why-hash-tables-should-use-prime-number-size/#respond) ![Intuition image](https://quickmathintuitions.org/wp-content/uploads/2016/06/My-aha-moments_float-e1466919792783.jpg) #### Categories - [Algebra](https://quickmathintuitions.org/category/algebra/) - [Analysis](https://quickmathintuitions.org/category/analysis/) - [Computer science](https://quickmathintuitions.org/category/computer-science/) - [Cryptography](https://quickmathintuitions.org/category/cryptography/) - [Finite Element Methods](https://quickmathintuitions.org/category/finite-element-methods/) - [Graph theory](https://quickmathintuitions.org/category/graph-theory/) - [Linear algebra](https://quickmathintuitions.org/category/linear-algebra/) - [Meta](https://quickmathintuitions.org/category/meta/) - [Modeling](https://quickmathintuitions.org/category/modeling/) - [Numerical Analysis](https://quickmathintuitions.org/category/numerical-analysis/) - [Probability](https://quickmathintuitions.org/category/probability/) - [Statistics](https://quickmathintuitions.org/category/statistics/) - [Uncategorized](https://quickmathintuitions.org/category/uncategorized/) #### [![RSS](https://quickmathintuitions.org/wp-includes/images/rss.png)](https://www.thecrowned.org/feeds/all-en.atom.xml) [Blog entries](https://thecrowned.org/) - [On Karpathy's "Software is changing (again)"](https://thecrowned.org/karpathy-software-is-changing) - [How many hours does it take to be pissed at France?](https://thecrowned.org/france-joke) - ["I'm really concerned about Hawai indigenous people's rights"](https://thecrowned.org/philosophy-of-science-class) - [Don't hurt pomegranates](https://thecrowned.org/pomegranate) - [What love tells me](https://thecrowned.org/mahler-love) - [The digital supermarket of human solitude (dating apps)](https://thecrowned.org/dating-apps) - [How Feldenkrais made me the best math teacher](https://thecrowned.org/feldenkrais-math) - [A cybersecurity take on the Swedish postal system](https://thecrowned.org/postnord-drama) - [The dread of teaching pointless math ruins generations](https://thecrowned.org/pointless-math) - [The differences between junior and senior software engineers](https://thecrowned.org/junior-vs-senior-engineers) Copyright © 2026 [Quick Math Intuitions](https://quickmathintuitions.org/ "Quick Math Intuitions"). [Proudly powered by WordPress](https://wordpress.org/) \| Theme: Apace by [ThemezHut](https://themezhut.com/themes/apace/).

Readable Markdown

I read in several books and online pages that hash tables should use a prime number for the size. Nobody really justified this statement properly. Here’s my attempt\! *** I believe that it just has to do with the fact that computers work with in base 2. Just think at how the same thing works for base 10: - 8 % 10 = 8 - 18 % 10 = 8 - 87865378 % 10 = 8 - 2387762348 % 10 = 8 It doesn’t matter what the number is: as long as it ends with 8, its modulo 10 will be 8. You could pick a huge power of 10 as modulo operator, such as 10^k (with k \> 10, let’s say), but 1. you would need a huge table to store the values 2. the hash function is still pretty stupid: it just trims the number retaining only the first *k* digits starting from the right. However, if you pick a different number as modulo operator, such as 12, then things are different: - 8 % 12 = 8 - 18 % 12 = 6 - 87865378 % 12 = 10 - 2387762348 % 12 = 8 We still have a collision, but the pattern becomes more complicated, and the collision is just due to the fact that 12 is still a small number. **Picking a big enough, non-power-of-two number will make sure the hash function really is a function of all the input bits, rather than a subset of them.** For example, with 367: - 8 % 367 = 8 - 18 % 367 = 18 - 87865378 % 367 = 73 - 2387762348 % 367 = 240 What is worth nothing is that there may be a pattern even with modulo 367, but it would be way less trivial than with modulo 10 (or with modulo 2 in binary). **We don’t really need a prime number**, just having a big non-power of two is enough. Having a prime number, obviously, is just a guaranteed way of satisfying those conditions. - Was this Helpful ? - [yes](https://quickmathintuitions.org/why-hash-tables-should-use-prime-number-size/) [no](https://quickmathintuitions.org/why-hash-tables-should-use-prime-number-size/) ## Post navigation

ML Classification

ML Categories

/Computers_and_Electronics		96.1%
/Computers_and_Electronics/Programming		79.2%

Raw JSON

{
    "/Computers_and_Electronics": 961,
    "/Computers_and_Electronics/Programming": 792
}

ML Page Types

/Article		99.9%
/Article/Tutorial_or_Guide		81.4%

Raw JSON

{
    "/Article": 999,
    "/Article/Tutorial_or_Guide": 814
}

ML Intent Types

Informational

99.9%

Raw JSON

{
    "Informational": 999
}

Content Metadata

Language

en-us

Author

Stefano Ottolenghi

Publish Time

2017-06-01 08:57:36 (8 years ago)

Original Publish Time

2017-06-01 08:57:36 (8 years ago)

Republished

Word Count (Total)

549

Word Count (Content)

336

Links

External Links

Internal Links

Technical SEO

Meta Nofollow

Meta Noarchive

JS Rendered

Redirect Target

null

Performance

Download Time (ms)

1,564

TTFB (ms)

1,564

Download Size (bytes)

12,137

Shard

43 (laksa)

Root Hash

18237700010392947643

Unparsed URL

org,quickmathintuitions!/why-hash-tables-should-use-prime-number-size/ s443