21979979 has 12 divisors (see below), whose sum is σ = 26915400. Its totient is φ = 17847648.

The previous prime is 21979957. The next prime is 21980003. The reversal of 21979979 is 97997912.

It is not a de Polignac number, because 21979979 - 2¹⁶ = 21914443 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21979979.

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 11 ways as a sum of consecutive naturals, for example, 10874 + ... + 12735.

It is an arithmetic number, because the mean of its divisors is an integer number (2242950).

Almost surely, 2^21979979 is an apocalyptic number.

21979979 is a deficient number, since it is larger than the sum of its proper divisors (4935421).

21979979 is a wasteful number, since it uses less digits than its factorization.

21979979 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23642 (or 23635 counting only the distinct ones).

The product of its digits is 642978, while the sum is 53.

The square root of 21979979 is about 4688.2810282661. The cubic root of 21979979 is about 280.1189078295.

The spelling of 21979979 in words is "twenty-one million, nine hundred seventy-nine thousand, nine hundred seventy-nine".