21857408 has 16 divisors (see below), whose sum is σ = 43544310. Its totient is φ = 10928640.

The previous prime is 21857389. The next prime is 21857411. The reversal of 21857408 is 80475812.

It can be written as a sum of positive squares in only one way, i.e., 18731584 + 3125824 = 4328^2 + 1768^2 .

It is a tau number, because it is divible by the number of its divisors (16).

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 85253 + ... + 85508.

Almost surely, 2^21857408 is an apocalyptic number.

It is an amenable number.

21857408 is a deficient number, since it is larger than the sum of its proper divisors (21686902).

21857408 is an equidigital number, since it uses as much as digits as its factorization.

21857408 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 170775 (or 170763 counting only the distinct ones).

The product of its (nonzero) digits is 17920, while the sum is 35.

The square root of 21857408 is about 4675.1906912981. The cubic root of 21857408 is about 279.5972440773.

The spelling of 21857408 in words is "twenty-one million, eight hundred fifty-seven thousand, four hundred eight".