21664464 has 20 divisors (see below), whose sum is σ = 55966656. Its totient is φ = 7221472.

The previous prime is 21664457. The next prime is 21664471. The reversal of 21664464 is 46446612.

It is an interprime number because it is at equal distance from previous prime (21664457) and next prime (21664471).

It is a nude number because it is divisible by every one of its digits.

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, 225624 + ... + 225719.

Almost surely, 2^21664464 is an apocalyptic number.

21664464 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21664464 is an abundant number, since it is smaller than the sum of its proper divisors (34302192).

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

21664464 is a wasteful number, since it uses less digits than its factorization.

21664464 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 451354 (or 451348 counting only the distinct ones).

The product of its digits is 27648, while the sum is 33.

The square root of 21664464 is about 4654.5100708882. The cubic root of 21664464 is about 278.7721061383.

The spelling of 21664464 in words is "twenty-one million, six hundred sixty-four thousand, four hundred sixty-four".