21857979 has 16 divisors (see below), whose sum is σ = 34239744. Its totient is φ = 12228000.

The previous prime is 21857959. The next prime is 21857993. The reversal of 21857979 is 97975812.

It is not a de Polignac number, because 21857979 - 2⁸ = 21857723 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21857959) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 25047 + ... + 25904.

It is an arithmetic number, because the mean of its divisors is an integer number (2139984).

Almost surely, 2^21857979 is an apocalyptic number.

21857979 is a deficient number, since it is larger than the sum of its proper divisors (12381765).

21857979 is a wasteful number, since it uses less digits than its factorization.

21857979 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50978.

The product of its digits is 317520, while the sum is 48.

The square root of 21857979 is about 4675.2517579271. The cubic root of 21857979 is about 279.5996787764.

The spelling of 21857979 in words is "twenty-one million, eight hundred fifty-seven thousand, nine hundred seventy-nine".