21979931 has 4 divisors (see below), whose sum is σ = 22138200. Its totient is φ = 21821664.

The previous prime is 21979913. The next prime is 21979939. The reversal of 21979931 is 13997912.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21979931 - 2¹⁴ = 21963547 is a prime.

It is a super-2 number, since 2×21979931² = 966234733529522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21979939) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 78926 + ... + 79203.

It is an arithmetic number, because the mean of its divisors is an integer number (5534550).

Almost surely, 2^21979931 is an apocalyptic number.

21979931 is a deficient number, since it is larger than the sum of its proper divisors (158269).

21979931 is a wasteful number, since it uses less digits than its factorization.

21979931 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 158268.

The product of its digits is 30618, while the sum is 41.

The square root of 21979931 is about 4688.2759091163. The cubic root of 21979931 is about 280.1187039209.

The spelling of 21979931 in words is "twenty-one million, nine hundred seventy-nine thousand, nine hundred thirty-one".