251516621 has 2 divisors, whose sum is σ = 251516622. Its totient is φ = 251516620.

The previous prime is 251516597. The next prime is 251516633. The reversal of 251516621 is 126615152.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 233784100 + 17732521 = 15290^2 + 4211^2 .

It is a cyclic number.

It is not a de Polignac number, because 251516621 - 2⁶ = 251516557 is a prime.

It is a super-2 number, since 2×251516621² = 126521221278515282, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (251516651) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 125758310 + 125758311.

It is an arithmetic number, because the mean of its divisors is an integer number (125758311).

Almost surely, 2^251516621 is an apocalyptic number.

It is an amenable number.

251516621 is a deficient number, since it is larger than the sum of its proper divisors (1).

251516621 is an equidigital number, since it uses as much as digits as its factorization.

251516621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3600, while the sum is 29.

The square root of 251516621 is about 15859.2755509197. The cubic root of 251516621 is about 631.2318394148.

The spelling of 251516621 in words is "two hundred fifty-one million, five hundred sixteen thousand, six hundred twenty-one".