21664900 has 18 divisors (see below), whose sum is σ = 47013050. Its totient is φ = 8665920.

The previous prime is 21664897. The next prime is 21664967. The reversal of 21664900 is 946612.

It can be written as a sum of positive squares in 3 ways, for example, as 5184 + 21659716 = 72^2 + 4654^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 108225 + ... + 108424.

Almost surely, 2^21664900 is an apocalyptic number.

21664900 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21664900 is an abundant number, since it is smaller than the sum of its proper divisors (25348150).

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

21664900 is a wasteful number, since it uses less digits than its factorization.

21664900 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 216663 (or 216656 counting only the distinct ones).

The product of its (nonzero) digits is 2592, while the sum is 28.

The square root of 21664900 is about 4654.5569069461. The cubic root of 21664900 is about 278.7739762334.

The spelling of 21664900 in words is "twenty-one million, six hundred sixty-four thousand, nine hundred".