21606664 has 8 divisors (see below), whose sum is σ = 40512510. Its totient is φ = 10803328.

The previous prime is 21606623. The next prime is 21606671. The reversal of 21606664 is 46660612.

It can be written as a sum of positive squares in only one way, i.e., 20520900 + 1085764 = 4530^2 + 1042^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1350409 + ... + 1350424.

Almost surely, 2^21606664 is an apocalyptic number.

It is an amenable number.

21606664 is a deficient number, since it is larger than the sum of its proper divisors (18905846).

21606664 is a wasteful number, since it uses less digits than its factorization.

21606664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2700839 (or 2700835 counting only the distinct ones).

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

The square root of 21606664 is about 4648.2968924112. The cubic root of 21606664 is about 278.5239673941.

The spelling of 21606664 in words is "twenty-one million, six hundred six thousand, six hundred sixty-four".