31 (number)

← 30 31 32 →
← 30 31 32 33 34 35 36 37 38 39 → List of numbers Integers ← 0 10 20 30 40 50 60 70 80 90 →
Cardinal	thirty-one
Ordinal	31st (thirty-first)
Factorization	prime
Prime	11th
Divisors	1, 31
Greek numeral	ΛΑ´
Roman numeral	XXXI, xxxi
Binary	111112
Ternary	10113
Senary	516
Octal	378
Duodecimal	2712
Hexadecimal	1F16

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 ^[1] (with 29), and a Mersenne prime. ^[2]

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.

References

1. Sloane, N. J. A. (ed.). "SequenceA077800(List of twin primes {p, p+2}.)". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved 2023-06-07.
2. Sloane, N. J. A. (ed.). "SequenceA000668(Mersenne primes (primes of the form 2^n - 1).)". The On-Line Encyclopedia of Integer Sequences . OEIS Foundation. Retrieved 2023-06-07.

External links

• Prime Curios! 31 from the Prime Pages