21660665 has 16 divisors (see below), whose sum is σ = 29467200. Its totient is φ = 15152832.

The previous prime is 21660643. The next prime is 21660677. The reversal of 21660665 is 56606612.

It is a cyclic number.

It is not a de Polignac number, because 21660665 - 2⁸ = 21660409 is a prime.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7535 + ... + 10004.

It is an arithmetic number, because the mean of its divisors is an integer number (1841700).

Almost surely, 2^21660665 is an apocalyptic number.

It is an amenable number.

21660665 is a deficient number, since it is larger than the sum of its proper divisors (7806535).

21660665 is a wasteful number, since it uses less digits than its factorization.

21660665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17576.

The product of its (nonzero) digits is 12960, while the sum is 32.

The square root of 21660665 is about 4654.1019541905. The cubic root of 21660665 is about 278.7558103718.

The spelling of 21660665 in words is "twenty-one million, six hundred sixty thousand, six hundred sixty-five".