21979815 has 32 divisors (see below), whose sum is σ = 41319936. Its totient is φ = 9836160.

The previous prime is 21979807. The next prime is 21979817. The reversal of 21979815 is 51897912.

It is not a de Polignac number, because 21979815 - 2³ = 21979807 is a prime.

It is a super-2 number, since 2×21979815² = 966224534868450, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21979817) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 2979 + ... + 7268.

It is an arithmetic number, because the mean of its divisors is an integer number (1291248).

Almost surely, 2^21979815 is an apocalyptic number.

21979815 is a deficient number, since it is larger than the sum of its proper divisors (19340121).

21979815 is a wasteful number, since it uses less digits than its factorization.

21979815 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10279.

The product of its digits is 45360, while the sum is 42.

The square root of 21979815 is about 4688.2635378144. The cubic root of 21979815 is about 280.1182111407.

The spelling of 21979815 in words is "twenty-one million, nine hundred seventy-nine thousand, eight hundred fifteen".