21087904 has 12 divisors (see below), whose sum is σ = 41516874. Its totient is φ = 10543936.

The previous prime is 21087889. The next prime is 21087917. The reversal of 21087904 is 40978012.

It can be written as a sum of positive squares in only one way, i.e., 14837904 + 6250000 = 3852^2 + 2500^2 .

It is a super-3 number, since 3×21087904³ (a number of 23 digits) contains 333 as substring. Note that it is a super-d number also for d = 2.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 329467 + ... + 329530.

Almost surely, 2^21087904 is an apocalyptic number.

It is an amenable number.

21087904 is a deficient number, since it is larger than the sum of its proper divisors (20428970).

21087904 is an equidigital number, since it uses as much as digits as its factorization.

21087904 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 659007 (or 658999 counting only the distinct ones).

The product of its (nonzero) digits is 4032, while the sum is 31.

The square root of 21087904 is about 4592.1567917483. The cubic root of 21087904 is about 276.2768348863.

The spelling of 21087904 in words is "twenty-one million, eighty-seven thousand, nine hundred four".