251665421 has 12 divisors (see below), whose sum is σ = 299896380. Its totient is φ = 210450240.

The previous prime is 251665417. The next prime is 251665429. The reversal of 251665421 is 124566152.

It can be written as a sum of positive squares in 2 ways, for example, as 79032100 + 172633321 = 8890^2 + 13139^2 .

It is not a de Polignac number, because 251665421 - 2² = 251665417 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (251665429) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 60626 + ... + 64643.

It is an arithmetic number, because the mean of its divisors is an integer number (24991365).

Almost surely, 2^251665421 is an apocalyptic number.

It is an amenable number.

251665421 is a deficient number, since it is larger than the sum of its proper divisors (48230959).

251665421 is a wasteful number, since it uses less digits than its factorization.

251665421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 125324 (or 125317 counting only the distinct ones).

The product of its digits is 14400, while the sum is 32.

The square root of 251665421 is about 15863.9661182190. The cubic root of 251665421 is about 631.3562961082.

The spelling of 251665421 in words is "two hundred fifty-one million, six hundred sixty-five thousand, four hundred twenty-one".