21646664 has 16 divisors (see below), whose sum is σ = 43709820. Its totient is φ = 9990720.

The previous prime is 21646633. The next prime is 21646721. The reversal of 21646664 is 46664612.

It can be written as a sum of positive squares in 2 ways, for example, as 21436900 + 209764 = 4630^2 + 458^2 .

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, 103967 + ... + 104174.

Almost surely, 2^21646664 is an apocalyptic number.

It is an amenable number.

21646664 is an abundant number, since it is smaller than the sum of its proper divisors (22063156).

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

21646664 is a wasteful number, since it uses less digits than its factorization.

21646664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 208160 (or 208156 counting only the distinct ones).

The product of its digits is 41472, while the sum is 35.

The square root of 21646664 is about 4652.5975540552. The cubic root of 21646664 is about 278.6957367881.

The spelling of 21646664 in words is "twenty-one million, six hundred forty-six thousand, six hundred sixty-four".