21664172 has 6 divisors (see below), whose sum is σ = 37912308. Its totient is φ = 10832084.

The previous prime is 21664169. The next prime is 21664177. The reversal of 21664172 is 27146612.

It is not an unprimeable number, because it can be changed into a prime (21664177) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2708018 + ... + 2708025.

It is an arithmetic number, because the mean of its divisors is an integer number (6318718).

Almost surely, 2^21664172 is an apocalyptic number.

It is an amenable number.

21664172 is a deficient number, since it is larger than the sum of its proper divisors (16248136).

21664172 is a wasteful number, since it uses less digits than its factorization.

21664172 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5416047 (or 5416045 counting only the distinct ones).

The product of its digits is 4032, while the sum is 29.

The square root of 21664172 is about 4654.4787033566. The cubic root of 21664172 is about 278.7708536752.

The spelling of 21664172 in words is "twenty-one million, six hundred sixty-four thousand, one hundred seventy-two".