21312864 has 72 divisors (see below), whose sum is σ = 62053992. Its totient is φ = 6935040.

The previous prime is 21312833. The next prime is 21312871. The reversal of 21312864 is 46821312.

It is a tau number, because it is divible by the number of its divisors (72).

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 11524 + ... + 13244.

It is an arithmetic number, because the mean of its divisors is an integer number (861861).

Almost surely, 2^21312864 is an apocalyptic number.

21312864 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21312864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31026996).

21312864 is an abundant number, since it is smaller than the sum of its proper divisors (40741128).

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

21312864 is a wasteful number, since it uses less digits than its factorization.

21312864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1780 (or 1769 counting only the distinct ones).

The product of its digits is 2304, while the sum is 27.

The square root of 21312864 is about 4616.5857513968. The cubic root of 21312864 is about 277.2557773356.

The spelling of 21312864 in words is "twenty-one million, three hundred twelve thousand, eight hundred sixty-four".