21178879 has 4 divisors (see below), whose sum is σ = 21286584. Its totient is φ = 21071176.

The previous prime is 21178867. The next prime is 21178891. The reversal of 21178879 is 97887112.

It is a happy number.

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

It is an interprime number because it is at equal distance from previous prime (21178867) and next prime (21178891).

It is a cyclic number.

It is not a de Polignac number, because 21178879 - 2⁵ = 21178847 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 (21178819) 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, 53557 + ... + 53950.

It is an arithmetic number, because the mean of its divisors is an integer number (5321646).

Almost surely, 2^21178879 is an apocalyptic number.

21178879 is a deficient number, since it is larger than the sum of its proper divisors (107705).

21178879 is a wasteful number, since it uses less digits than its factorization.

21178879 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 107704.

The product of its digits is 56448, while the sum is 43.

The square root of 21178879 is about 4602.0516077072. The cubic root of 21178879 is about 276.6735588032.

The spelling of 21178879 in words is "twenty-one million, one hundred seventy-eight thousand, eight hundred seventy-nine".