21428879 has 4 divisors (see below), whose sum is σ = 21470376. Its totient is φ = 21387384.

The previous prime is 21428861. The next prime is 21428887. The reversal of 21428879 is 97882412.

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 21428879 - 2²⁴ = 4651663 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 (21428579) 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, 19964 + ... + 21009.

It is an arithmetic number, because the mean of its divisors is an integer number (5367594).

Almost surely, 2^21428879 is an apocalyptic number.

21428879 is a deficient number, since it is larger than the sum of its proper divisors (41497).

21428879 is an equidigital number, since it uses as much as digits as its factorization.

21428879 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41496.

The product of its digits is 64512, while the sum is 41.

The square root of 21428879 is about 4629.1337202548. The cubic root of 21428879 is about 277.7579410486.

The spelling of 21428879 in words is "twenty-one million, four hundred twenty-eight thousand, eight hundred seventy-nine".