21356631 has 6 divisors (see below), whose sum is σ = 30848480. Its totient is φ = 14237748.

The previous prime is 21356611. The next prime is 21356633. The reversal of 21356631 is 13665312.

21356631 is a `hidden beast` number, since 21 + 3 + 5 + 6 + 631 = 666.

It is not a de Polignac number, because 21356631 - 2⁶ = 21356567 is a prime.

It is a super-2 number, since 2×21356631² = 912211375340322, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21356595 and 21356604.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21356633) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1186471 + ... + 1186488.

Almost surely, 2^21356631 is an apocalyptic number.

21356631 is a deficient number, since it is larger than the sum of its proper divisors (9491849).

21356631 is a wasteful number, since it uses less digits than its factorization.

21356631 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2372965 (or 2372962 counting only the distinct ones).

The product of its digits is 3240, while the sum is 27.

The square root of 21356631 is about 4621.3235117226. The cubic root of 21356631 is about 277.4454336343.

The spelling of 21356631 in words is "twenty-one million, three hundred fifty-six thousand, six hundred thirty-one".