21664920 has 32 divisors (see below), whose sum is σ = 64995120. Its totient is φ = 5777280.

The previous prime is 21664897. The next prime is 21664967. The reversal of 21664920 is 2946612.

21664920 = T₁₅₁ + T₁₅₂ + ... + T₅₁₀.

It is a Harshad number since it is a multiple of its sum of digits (30).

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, 90151 + ... + 90390.

Almost surely, 2^21664920 is an apocalyptic number.

21664920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21664920 is an abundant number, since it is smaller than the sum of its proper divisors (43330200).

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

21664920 is a wasteful number, since it uses less digits than its factorization.

21664920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 180555 (or 180551 counting only the distinct ones).

The product of its (nonzero) digits is 5184, while the sum is 30.

The square root of 21664920 is about 4654.5590553779. The cubic root of 21664920 is about 278.7740620169.

The spelling of 21664920 in words is "twenty-one million, six hundred sixty-four thousand, nine hundred twenty".