31 (number)

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title: "31 (number)" type: doc version: 1 created: 2026-02-28 author: "Wikipedia contributors" status: active scope: public tags: ["integers"] topic_path: "general/integers" source: "https://en.wikipedia.org/wiki/31_(number)" license: "CC BY-SA 4.0" wikipedia_page_id: 0 wikipedia_revision_id: 0

::data[format=table title="Infobox number"]

FieldValue
number31
factorizationprime
prime11th
divisor1, 31
::

| number = 31 | factorization = prime | prime = 11th | divisor = 1, 31

31 (thirty-one) is the natural number following 30 and preceding 32. It is a prime number.

Mathematics

31 is a prime number, a twin prime (with 29), and a Mersenne prime.

::figure[src="https://upload.wikimedia.org/wikipedia/commons/9/94/Centered_pentagonal_number_31.svg" caption="31 is a [[centered pentagonal number]]."] ::

In other fields

31 equal temperament is a popular microtonal tuning for musical instruments because it provides a good approximation of harmonic intervals.

January, March, May, July, August, October and December have 31 days.

California was the 31st state to join the United States.

31 is the international calling code for the Netherlands.

Notes

References

References

  1. {{Cite OEIS. A077800. List of twin primes {p, p+2}.
  2. {{Cite OEIS. A000668. Mersenne primes (primes of the form 2^n - 1).

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integers