21566864 has 40 divisors (see below), whose sum is σ = 45851232. Its totient is φ = 9745920.

The previous prime is 21566837. The next prime is 21566873. The reversal of 21566864 is 46866512.

It is a congruent number.

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, 49592 + ... + 50024.

Almost surely, 2^21566864 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 21566864, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22925616).

21566864 is an abundant number, since it is smaller than the sum of its proper divisors (24284368).

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

21566864 is a wasteful number, since it uses less digits than its factorization.

21566864 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 735 (or 729 counting only the distinct ones).

The product of its digits is 69120, while the sum is 38.

The square root of 21566864 is about 4644.0137812026. The cubic root of 21566864 is about 278.3528463099.

The spelling of 21566864 in words is "twenty-one million, five hundred sixty-six thousand, eight hundred sixty-four".