20979857 has 4 divisors (see below), whose sum is σ = 22084080. Its totient is φ = 19875636.

The previous prime is 20979809. The next prime is 20979877. The reversal of 20979857 is 75897902.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 20979857 - 2¹⁴ = 20963473 is a prime.

It is not an unprimeable number, because it can be changed into a prime (20979877) 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, 552083 + ... + 552120.

It is an arithmetic number, because the mean of its divisors is an integer number (5521020).

Almost surely, 2^20979857 is an apocalyptic number.

It is an amenable number.

20979857 is a deficient number, since it is larger than the sum of its proper divisors (1104223).

20979857 is a wasteful number, since it uses less digits than its factorization.

20979857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1104222.

The product of its (nonzero) digits is 317520, while the sum is 47.

The square root of 20979857 is about 4580.3773861987. The cubic root of 20979857 is about 275.8041782928.

The spelling of 20979857 in words is "twenty million, nine hundred seventy-nine thousand, eight hundred fifty-seven".