21656564 has 12 divisors (see below), whose sum is σ = 37959264. Its totient is φ = 10811064.

The previous prime is 21656543. The next prime is 21656597. The reversal of 21656564 is 46565612.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1232 + ... + 6695.

It is an arithmetic number, because the mean of its divisors is an integer number (3163272).

Almost surely, 2^21656564 is an apocalyptic number.

It is an amenable number.

21656564 is a deficient number, since it is larger than the sum of its proper divisors (16302700).

21656564 is a wasteful number, since it uses less digits than its factorization.

21656564 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8614 (or 8612 counting only the distinct ones).

The product of its digits is 43200, while the sum is 35.

The square root of 21656564 is about 4653.6613542457. The cubic root of 21656564 is about 278.7382170410.

The spelling of 21656564 in words is "twenty-one million, six hundred fifty-six thousand, five hundred sixty-four".