21564172 has 24 divisors (see below), whose sum is σ = 43464960. Its totient is φ = 9169680.

The previous prime is 21564149. The next prime is 21564181. The reversal of 21564172 is 27146512.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a self number, because there is not a number n which added to its sum of digits gives 21564172.

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, 729 + ... + 6607.

It is an arithmetic number, because the mean of its divisors is an integer number (1811040).

Almost surely, 2^21564172 is an apocalyptic number.

It is an amenable number.

21564172 is an abundant number, since it is smaller than the sum of its proper divisors (21900788).

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

21564172 is a wasteful number, since it uses less digits than its factorization.

21564172 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6021 (or 6019 counting only the distinct ones).

The product of its digits is 3360, while the sum is 28.

The square root of 21564172 is about 4643.7239366698. The cubic root of 21564172 is about 278.3412643905.

It can be divided in two parts, 21564 and 172, that added together give a triangular number (21736 = T₂₀₈).

The spelling of 21564172 in words is "twenty-one million, five hundred sixty-four thousand, one hundred seventy-two".