21856579 has 2 divisors, whose sum is σ = 21856580. Its totient is φ = 21856578.

The previous prime is 21856537. The next prime is 21856589. The reversal of 21856579 is 97565812.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21856579 - 2⁷ = 21856451 is a prime.

It is not a weakly prime, because it can be changed into another prime (21856589) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10928289 + 10928290.

It is an arithmetic number, because the mean of its divisors is an integer number (10928290).

Almost surely, 2^21856579 is an apocalyptic number.

21856579 is a deficient number, since it is larger than the sum of its proper divisors (1).

21856579 is an equidigital number, since it uses as much as digits as its factorization.

21856579 is an evil number, because the sum of its binary digits is even.

The product of its digits is 151200, while the sum is 43.

The square root of 21856579 is about 4675.1020309722. The cubic root of 21856579 is about 279.5937092109.

It can be divided in two parts, 2 and 1856579, that added together give a palindrome (1856581).

The spelling of 21856579 in words is "twenty-one million, eight hundred fifty-six thousand, five hundred seventy-nine".