21684564 has 48 divisors (see below), whose sum is σ = 61333440. Its totient is φ = 6570720.

The previous prime is 21684557. The next prime is 21684589. The reversal of 21684564 is 46548612.

21684564 is a `hidden beast` number, since 2 + 16 + 84 + 564 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

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 15 ways as a sum of consecutive naturals, for example, 7939 + ... + 10314.

It is an arithmetic number, because the mean of its divisors is an integer number (1277780).

Almost surely, 2^21684564 is an apocalyptic number.

It is an amenable number.

21684564 is an abundant number, since it is smaller than the sum of its proper divisors (39648876).

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

21684564 is a wasteful number, since it uses less digits than its factorization.

21684564 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18277 (or 18269 counting only the distinct ones).

The product of its digits is 46080, while the sum is 36.

The square root of 21684564 is about 4656.6687664037. The cubic root of 21684564 is about 278.8582931668.

The spelling of 21684564 in words is "twenty-one million, six hundred eighty-four thousand, five hundred sixty-four".