21565664 has 24 divisors (see below), whose sum is σ = 42751800. Its totient is φ = 10708096.

The previous prime is 21565633. The next prime is 21565667. The reversal of 21565664 is 46656512.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21565667) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2507 + ... + 7029.

It is an arithmetic number, because the mean of its divisors is an integer number (1781325).

Almost surely, 2^21565664 is an apocalyptic number.

It is an amenable number.

21565664 is a deficient number, since it is larger than the sum of its proper divisors (21186136).

21565664 is a wasteful number, since it uses less digits than its factorization.

21565664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4682 (or 4674 counting only the distinct ones).

The product of its digits is 43200, while the sum is 35.

The square root of 21565664 is about 4643.8845808224. The cubic root of 21565664 is about 278.3476836120.

The spelling of 21565664 in words is "twenty-one million, five hundred sixty-five thousand, six hundred sixty-four".