21631251 has 8 divisors (see below), whose sum is σ = 29097360. Its totient is φ = 14292992.

The previous prime is 21631243. The next prime is 21631283. The reversal of 21631251 is 15213612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21631251 - 2³ = 21631243 is a prime.

It is a super-2 number, since 2×21631251² = 935822039650002, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21630251) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 31566 + ... + 32243.

It is an arithmetic number, because the mean of its divisors is an integer number (3637170).

Almost surely, 2^21631251 is an apocalyptic number.

21631251 is a deficient number, since it is larger than the sum of its proper divisors (7466109).

21631251 is a wasteful number, since it uses less digits than its factorization.

21631251 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 63925.

The product of its digits is 360, while the sum is 21.

The square root of 21631251 is about 4650.9408725547. The cubic root of 21631251 is about 278.6295748257.

Adding to 21631251 its reverse (15213612), we get a palindrome (36844863).

The spelling of 21631251 in words is "twenty-one million, six hundred thirty-one thousand, two hundred fifty-one".