21388624 has 20 divisors (see below), whose sum is σ = 41581044. Its totient is φ = 10658048.

The previous prime is 21388607. The next prime is 21388639. The reversal of 21388624 is 42688312.

It can be written as a sum of positive squares in 2 ways, for example, as 9610000 + 11778624 = 3100^2 + 3432^2 .

It is a super-2 number, since 2×21388624² = 914946473226752, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21388624.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2964 + ... + 7180.

Almost surely, 2^21388624 is an apocalyptic number.

It is an amenable number.

21388624 is a deficient number, since it is larger than the sum of its proper divisors (20192420).

21388624 is a wasteful number, since it uses less digits than its factorization.

21388624 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4542 (or 4536 counting only the distinct ones).

The product of its digits is 18432, while the sum is 34.

The square root of 21388624 is about 4624.7836706164. The cubic root of 21388624 is about 277.5839055855.

The spelling of 21388624 in words is "twenty-one million, three hundred eighty-eight thousand, six hundred twenty-four".