21664556 has 12 divisors (see below), whose sum is σ = 38719968. Its totient is φ = 10601712.

The previous prime is 21664529. The next prime is 21664607. The reversal of 21664556 is 65546612.

21664556 = T₃₈₃ + T₃₈₄ + ... + T₅₇₀.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 57431 + ... + 57806.

It is an arithmetic number, because the mean of its divisors is an integer number (3226664).

Almost surely, 2^21664556 is an apocalyptic number.

It is an amenable number.

21664556 is a deficient number, since it is larger than the sum of its proper divisors (17055412).

21664556 is a wasteful number, since it uses less digits than its factorization.

21664556 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 115288 (or 115286 counting only the distinct ones).

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

The square root of 21664556 is about 4654.5199537654. The cubic root of 21664556 is about 278.7725007476.

The spelling of 21664556 in words is "twenty-one million, six hundred sixty-four thousand, five hundred fifty-six".