251 (number)

In mathematics

• a Sophie Germain prime.
• the sum of three consecutive primes and seven consecutive primes.
• 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:

In science

• The average atomic mass and most stable isotope of Californium, which has a half life of about 900 years.