21566564 has 12 divisors (see below), whose sum is σ = 38619504. Its totient is φ = 10532424.

The previous prime is 21566551. The next prime is 21566593. The reversal of 21566564 is 46566512.

It is a hoax number, since the sum of its digits (35) coincides with the sum of the digits of its distinct prime factors.

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, 62522 + ... + 62865.

It is an arithmetic number, because the mean of its divisors is an integer number (3218292).

Almost surely, 2^21566564 is an apocalyptic number.

It is an amenable number.

21566564 is a deficient number, since it is larger than the sum of its proper divisors (17052940).

21566564 is a wasteful number, since it uses less digits than its factorization.

21566564 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 125434 (or 125432 counting only the distinct ones).

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

The square root of 21566564 is about 4643.9814814446. The cubic root of 21566564 is about 278.3515556534.

The spelling of 21566564 in words is "twenty-one million, five hundred sixty-six thousand, five hundred sixty-four".