Sophie Germain prime
131 is a Sophie Germain prime, an irregular prime, 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 formula_1. Because the next odd number, 133, is a semiprime, 131 is a Chen prime. 131 is an Ulam number.