21664565 has 16 divisors (see below), whose sum is σ = 28358400. Its totient is φ = 15792192.

The previous prime is 21664529. The next prime is 21664607. The reversal of 21664565 is 56546612.

21664565 = 342² + 343² + ... + 471².

It is not a de Polignac number, because 21664565 - 2⁶ = 21664501 is a prime.

It is a Curzon number.

It is a plaindrome in base 11.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 3026 + ... + 7244.

It is an arithmetic number, because the mean of its divisors is an integer number (1772400).

Almost surely, 2^21664565 is an apocalyptic number.

It is an amenable number.

21664565 is a deficient number, since it is larger than the sum of its proper divisors (6693835).

21664565 is a wasteful number, since it uses less digits than its factorization.

21664565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4316.

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

The square root of 21664565 is about 4654.5209205674. The cubic root of 21664565 is about 278.7725393506.

The spelling of 21664565 in words is "twenty-one million, six hundred sixty-four thousand, five hundred sixty-five".