21987879 has 16 divisors (see below), whose sum is σ = 30393312. Its totient is φ = 14128128.

The previous prime is 21987871. The next prime is 21987899. The reversal of 21987879 is 97878912.

It is not a de Polignac number, because 21987879 - 2³ = 21987871 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21987871) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11667 + ... + 13419.

It is an arithmetic number, because the mean of its divisors is an integer number (1899582).

Almost surely, 2^21987879 is an apocalyptic number.

21987879 is a deficient number, since it is larger than the sum of its proper divisors (8405433).

21987879 is a wasteful number, since it uses less digits than its factorization.

21987879 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1906.

The product of its digits is 508032, while the sum is 51.

The square root of 21987879 is about 4689.1234788604. The cubic root of 21987879 is about 280.1524637351.

The spelling of 21987879 in words is "twenty-one million, nine hundred eighty-seven thousand, eight hundred seventy-nine".