21604056 has 16 divisors (see below), whose sum is σ = 54010200. Its totient is φ = 7201344.

The previous prime is 21604031. The next prime is 21604057. The reversal of 21604056 is 65040612.

It is a super-2 number, since 2×21604056² = 933470471302272, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (24), and also a Moran number because the ratio is a prime number: 900169 = 21604056 / (2 + 1 + 6 + 0 + 4 + 0 + 5 + 6).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21604057) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 450061 + ... + 450108.

Almost surely, 2^21604056 is an apocalyptic number.

It is an amenable number.

21604056 is an abundant number, since it is smaller than the sum of its proper divisors (32406144).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21604056 is a wasteful number, since it uses less digits than its factorization.

21604056 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 900178 (or 900174 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 24.

The square root of 21604056 is about 4648.0163510900. The cubic root of 21604056 is about 278.5127606705.

Adding to 21604056 its reverse (65040612), we get a palindrome (86644668).

It can be divided in two parts, 2160 and 4056, that added together give a triangular number (6216 = T₁₁₁).

The spelling of 21604056 in words is "twenty-one million, six hundred four thousand, fifty-six".