21561388 has 12 divisors (see below), whose sum is σ = 37769200. Its totient is φ = 10770192.

The previous prime is 21561383. The next prime is 21561401. The reversal of 21561388 is 88316512.

It is not an unprimeable number, because it can be changed into a prime (21561383) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3670 + ... + 7522.

Almost surely, 2^21561388 is an apocalyptic number.

It is an amenable number.

21561388 is a deficient number, since it is larger than the sum of its proper divisors (16207812).

21561388 is a wasteful number, since it uses less digits than its factorization.

21561388 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5256 (or 5254 counting only the distinct ones).

The product of its digits is 11520, while the sum is 34.

The square root of 21561388 is about 4643.4241675729. The cubic root of 21561388 is about 278.3292856412.

The spelling of 21561388 in words is "twenty-one million, five hundred sixty-one thousand, three hundred eighty-eight".