21566538 has 24 divisors (see below), whose sum is σ = 53403168. Its totient is φ = 6161832.

The previous prime is 21566509. The next prime is 21566543. The reversal of 21566538 is 83566512.

It is a super-2 number, since 2×21566538² = 930231122610888, which contains 22 as substring.

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, 85456 + ... + 85707.

It is an arithmetic number, because the mean of its divisors is an integer number (2225132).

Almost surely, 2^21566538 is an apocalyptic number.

21566538 is an abundant number, since it is smaller than the sum of its proper divisors (31836630).

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

21566538 is a wasteful number, since it uses less digits than its factorization.

21566538 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 171178 (or 171175 counting only the distinct ones).

The product of its digits is 43200, while the sum is 36.

The square root of 21566538 is about 4643.9786821216. The cubic root of 21566538 is about 278.3514437959.

The spelling of 21566538 in words is "twenty-one million, five hundred sixty-six thousand, five hundred thirty-eight".