21660664 has 16 divisors (see below), whose sum is σ = 42379920. Its totient is φ = 10359360.

The previous prime is 21660643. The next prime is 21660677. The reversal of 21660664 is 46606612.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 58677 + ... + 59044.

It is an arithmetic number, because the mean of its divisors is an integer number (2648745).

Almost surely, 2^21660664 is an apocalyptic number.

It is an amenable number.

21660664 is a deficient number, since it is larger than the sum of its proper divisors (20719256).

21660664 is a wasteful number, since it uses less digits than its factorization.

21660664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 117750 (or 117746 counting only the distinct ones).

The product of its (nonzero) digits is 10368, while the sum is 31.

The square root of 21660664 is about 4654.1018467584. The cubic root of 21660664 is about 278.7558060820.

The spelling of 21660664 in words is "twenty-one million, six hundred sixty thousand, six hundred sixty-four".