131 (number)

131 (one hundred thirty one) is the natural number following 130 and preceding 132.

← 130 131 132 →
← 130 131 132 133 134 135 136 137 138 139 → List of numbers Integers ← 0 100 200 300 400 500 600 700 800 900 →
Cardinal	one hundred thirty-one
Ordinal	131st (one hundred thirty-first)
Factorization	prime
Prime	32nd
Divisors	1, 131
Greek numeral	ΡΛΑ´
Roman numeral	CXXXI, cxxxi
Binary	100000112
Ternary	112123
Senary	3356
Octal	2038
Duodecimal	AB12
Hexadecimal	8316

In mathematics

131 is a Sophie Germain prime,^[1] an irregular prime,^[2] the second 3-digit palindromic prime, and also a permutable prime with 113 and 311. It can be expressed as the sum of three consecutive primes, 131 = 41 + 43 + 47. 131 is an Eisenstein prime with no imaginary part and real part of the form ${\displaystyle 3n-1}$. Because the next odd number, 133, is a semiprime, 131 is a Chen prime. 131 is an Ulam number.^[3]

131 is a full reptend prime in base 10 (and also in base 2). The decimal expansion of 1/131 repeats the digits 007633587786259541984732824427480916030534351145038167938931 297709923664122137404580152671755725190839694656488549618320 6106870229 indefinitely.

131 is the fifth discriminant of imaginary quadratic fields with class number 5, where the 131st prime number 739 is the fifteenth such discriminant.^[4] Meanwhile, there are conjectured to be a total of 131 discriminants of class number 8 (only one more discriminant could exist).^[5]