21645972 has 36 divisors (see below), whose sum is σ = 55618836. Its totient is φ = 7096320.

The previous prime is 21645937. The next prime is 21646003. The reversal of 21645972 is 27954612.

21645972 is a `hidden beast` number, since 2 + 1 + 64 + 597 + 2 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 3549456 + 18096516 = 1884^2 + 4254^2 .

It is a tau number, because it is divible by the number of its divisors (36).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2733 + ... + 7124.

Almost surely, 2^21645972 is an apocalyptic number.

It is an amenable number.

21645972 is an abundant number, since it is smaller than the sum of its proper divisors (33972864).

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

21645972 is a wasteful number, since it uses less digits than its factorization.

21645972 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9928 (or 9923 counting only the distinct ones).

The product of its digits is 30240, while the sum is 36.

The square root of 21645972 is about 4652.5231864011. The cubic root of 21645972 is about 278.6927669771.

The spelling of 21645972 in words is "twenty-one million, six hundred forty-five thousand, nine hundred seventy-two".