21308864 has 14 divisors (see below), whose sum is σ = 42284904. Its totient is φ = 10654400.

The previous prime is 21308831. The next prime is 21308867. The reversal of 21308864 is 46880312.

It is a Harshad number since it is a multiple of its sum of digits (32).

It is a self number, because there is not a number n which added to its sum of digits gives 21308864.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21308867) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 166412 + ... + 166539.

Almost surely, 2^21308864 is an apocalyptic number.

It is an amenable number.

21308864 is a deficient number, since it is larger than the sum of its proper divisors (20976040).

21308864 is an equidigital number, since it uses as much as digits as its factorization.

21308864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 332963 (or 332953 counting only the distinct ones).

The product of its (nonzero) digits is 9216, while the sum is 32.

The square root of 21308864 is about 4616.1525104788. The cubic root of 21308864 is about 277.2384311216.

The spelling of 21308864 in words is "twenty-one million, three hundred eight thousand, eight hundred sixty-four".