21987564 has 48 divisors (see below), whose sum is σ = 52690176. Its totient is φ = 7134400.

The previous prime is 21987557. The next prime is 21987571. The reversal of 21987564 is 46578912.

It is an interprime number because it is at equal distance from previous prime (21987557) and next prime (21987571).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 111514 + ... + 111710.

It is an arithmetic number, because the mean of its divisors is an integer number (1097712).

Almost surely, 2^21987564 is an apocalyptic number.

It is an amenable number.

21987564 is an abundant number, since it is smaller than the sum of its proper divisors (30702612).

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

21987564 is a wasteful number, since it uses less digits than its factorization.

21987564 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 406 (or 404 counting only the distinct ones).

The product of its digits is 120960, while the sum is 42.

The square root of 21987564 is about 4689.0898903732. The cubic root of 21987564 is about 280.1511259003.

The spelling of 21987564 in words is "twenty-one million, nine hundred eighty-seven thousand, five hundred sixty-four".