21387939 has 8 divisors (see below), whose sum is σ = 30018240. Its totient is φ = 13508136.

The previous prime is 21387931. The next prime is 21387959. The reversal of 21387939 is 93978312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21387939 - 2³ = 21387931 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21387939.

It is not an unprimeable number, because it can be changed into a prime (21387931) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 187557 + ... + 187670.

It is an arithmetic number, because the mean of its divisors is an integer number (3752280).

Almost surely, 2^21387939 is an apocalyptic number.

21387939 is a deficient number, since it is larger than the sum of its proper divisors (8630301).

21387939 is a wasteful number, since it uses less digits than its factorization.

21387939 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 375249.

The product of its digits is 81648, while the sum is 42.

The square root of 21387939 is about 4624.7096125054. The cubic root of 21387939 is about 277.5809422189.

The spelling of 21387939 in words is "twenty-one million, three hundred eighty-seven thousand, nine hundred thirty-nine".