21387968 has 28 divisors (see below), whose sum is σ = 48505872. Its totient is φ = 9166080.

The previous prime is 21387959. The next prime is 21387973. The reversal of 21387968 is 86978312.

It is a tau number, because it is divible by the number of its divisors (28).

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 23423 + ... + 24318.

Almost surely, 2^21387968 is an apocalyptic number.

21387968 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21387968 is an abundant number, since it is smaller than the sum of its proper divisors (27117904).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21387968 is an equidigital number, since it uses as much as digits as its factorization.

21387968 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 47760 (or 47750 counting only the distinct ones).

The product of its digits is 145152, while the sum is 44.

The square root of 21387968 is about 4624.7127478363. The cubic root of 21387968 is about 277.5810676766.

The spelling of 21387968 in words is "twenty-one million, three hundred eighty-seven thousand, nine hundred sixty-eight".