21664408 has 16 divisors (see below), whose sum is σ = 42759000. Its totient is φ = 10262016.

The previous prime is 21664373. The next prime is 21664417. The reversal of 21664408 is 80446612.

It is a self number, because there is not a number n which added to its sum of digits gives 21664408.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 71113 + ... + 71416.

Almost surely, 2^21664408 is an apocalyptic number.

It is an amenable number.

21664408 is a deficient number, since it is larger than the sum of its proper divisors (21094592).

21664408 is a wasteful number, since it uses less digits than its factorization.

21664408 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 142554 (or 142550 counting only the distinct ones).

The product of its (nonzero) digits is 9216, while the sum is 31.

The square root of 21664408 is about 4654.5040552136. The cubic root of 21664408 is about 278.7718659408.

The spelling of 21664408 in words is "twenty-one million, six hundred sixty-four thousand, four hundred eight".