251

251 is: a Sophie Germain prime. the sum of three consecutive primes (79 + 83 + 89) and seven consecutive primes (23 + 29 + 31 + 37 + 41 + 43 + 47). a Chen prime. an Eisenstein prime with no imaginary part. a de Polignac number, meaning that it is odd and cannot be formed by adding a power of two to a prime number. the smallest number that can be formed in more than one way by summing three positive cubes: 251 = 2 3 + 3 3 + 6 3 = 1 3 + 5 3 + 5 3 . {\displaystyle 251=2^{3}+3^{3}+6^{3}=1^{3}+5^{3}+5^{3}.}