21556864 has 64 divisors (see below), whose sum is σ = 50184000. Its totient is φ = 9219840.

The previous prime is 21556859. The next prime is 21556883. The reversal of 21556864 is 46865512.

It is a tau number, because it is divible by the number of its divisors (64).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 43659 + ... + 44149.

It is an arithmetic number, because the mean of its divisors is an integer number (784125).

Almost surely, 2^21556864 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21556864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25092000).

21556864 is an abundant number, since it is smaller than the sum of its proper divisors (28627136).

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

21556864 is an frugal number, since it uses more digits than its factorization.

21556864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 526 (or 500 counting only the distinct ones).

The product of its digits is 57600, while the sum is 37.

The square root of 21556864 is about 4642.9370015110. The cubic root of 21556864 is about 278.3098179742.

The spelling of 21556864 in words is "twenty-one million, five hundred fifty-six thousand, eight hundred sixty-four".