21557879 has 4 divisors (see below), whose sum is σ = 24637584. Its totient is φ = 18478176.

The previous prime is 21557843. The next prime is 21557917. The reversal of 21557879 is 97875512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21557879 - 2⁸ = 21557623 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 (21557579) 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, 1539842 + ... + 1539855.

It is an arithmetic number, because the mean of its divisors is an integer number (6159396).

Almost surely, 2^21557879 is an apocalyptic number.

21557879 is a deficient number, since it is larger than the sum of its proper divisors (3079705).

21557879 is an equidigital number, since it uses as much as digits as its factorization.

21557879 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3079704.

The product of its digits is 176400, while the sum is 44.

The square root of 21557879 is about 4643.0463060366. The cubic root of 21557879 is about 278.3141859570.

The spelling of 21557879 in words is "twenty-one million, five hundred fifty-seven thousand, eight hundred seventy-nine".