21639408 has 40 divisors (see below), whose sum is σ = 63888768. Its totient is φ = 6182592.

The previous prime is 21639383. The next prime is 21639427. The reversal of 21639408 is 80493612.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 31866 + ... + 32537.

Almost surely, 2^21639408 is an apocalyptic number.

21639408 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21639408 is an abundant number, since it is smaller than the sum of its proper divisors (42249360).

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

21639408 is a wasteful number, since it uses less digits than its factorization.

21639408 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 64421 (or 64415 counting only the distinct ones).

The product of its (nonzero) digits is 10368, while the sum is 33.

The square root of 21639408 is about 4651.8177092401. The cubic root of 21639408 is about 278.6645935404.

The spelling of 21639408 in words is "twenty-one million, six hundred thirty-nine thousand, four hundred eight".