21756879 has 6 divisors (see below), whose sum is σ = 31426616. Its totient is φ = 14504580.

The previous prime is 21756863. The next prime is 21756883. The reversal of 21756879 is 97865712.

21756879 is a `hidden beast` number, since 2 + 17 + 568 + 79 = 666.

It is not a de Polignac number, because 21756879 - 2⁴ = 21756863 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21756829) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1208707 + ... + 1208724.

Almost surely, 2^21756879 is an apocalyptic number.

21756879 is a deficient number, since it is larger than the sum of its proper divisors (9669737).

21756879 is a wasteful number, since it uses less digits than its factorization.

21756879 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2417437 (or 2417434 counting only the distinct ones).

The product of its digits is 211680, while the sum is 45.

The square root of 21756879 is about 4664.4269744525. The cubic root of 21756879 is about 279.1679337385.

It can be divided in two parts, 21 and 756879, that added together give a square (756900 = 870²).

The spelling of 21756879 in words is "twenty-one million, seven hundred fifty-six thousand, eight hundred seventy-nine".