21604864 has 20 divisors (see below), whose sum is σ = 43168554. Its totient is φ = 10802176.

The previous prime is 21604853. The next prime is 21604871. The reversal of 21604864 is 46840612.

It can be written as a sum of positive squares in only one way, i.e., 21086464 + 518400 = 4592^2 + 720^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 20587 + ... + 21610.

Almost surely, 2^21604864 is an apocalyptic number.

It is an amenable number.

21604864 is a deficient number, since it is larger than the sum of its proper divisors (21563690).

21604864 is an frugal number, since it uses more digits than its factorization.

21604864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42215 (or 42199 counting only the distinct ones).

The product of its (nonzero) digits is 9216, while the sum is 31.

The square root of 21604864 is about 4648.1032690765. The cubic root of 21604864 is about 278.5162327887.

The spelling of 21604864 in words is "twenty-one million, six hundred four thousand, eight hundred sixty-four".