21087879 has 4 divisors (see below), whose sum is σ = 28117176. Its totient is φ = 14058584.

The previous prime is 21087863. The next prime is 21087889. The reversal of 21087879 is 97878012.

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 21087879 - 2⁴ = 21087863 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21087879.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21087809) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3514644 + ... + 3514649.

It is an arithmetic number, because the mean of its divisors is an integer number (7029294).

Almost surely, 2^21087879 is an apocalyptic number.

21087879 is a deficient number, since it is larger than the sum of its proper divisors (7029297).

21087879 is an equidigital number, since it uses as much as digits as its factorization.

21087879 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7029296.

The product of its (nonzero) digits is 56448, while the sum is 42.

The square root of 21087879 is about 4592.1540697150. The cubic root of 21087879 is about 276.2767257096.

The spelling of 21087879 in words is "twenty-one million, eighty-seven thousand, eight hundred seventy-nine".