21664331 has 4 divisors (see below), whose sum is σ = 23330832. Its totient is φ = 19997832.

The previous prime is 21664327. The next prime is 21664339. The reversal of 21664331 is 13346612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21664331 - 2² = 21664327 is a prime.

It is a super-2 number, since 2×21664331² = 938686475355122, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21664331.

It is not an unprimeable number, because it can be changed into a prime (21664339) 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 in 3 ways as a sum of consecutive naturals, for example, 833231 + ... + 833256.

It is an arithmetic number, because the mean of its divisors is an integer number (5832708).

Almost surely, 2^21664331 is an apocalyptic number.

21664331 is a deficient number, since it is larger than the sum of its proper divisors (1666501).

21664331 is a wasteful number, since it uses less digits than its factorization.

21664331 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1666500.

The product of its digits is 2592, while the sum is 26.

The square root of 21664331 is about 4654.4957836483. The cubic root of 21664331 is about 278.7715356685.

It can be divided in two parts, 2166 and 4331, that multiplied together give a triangular number (9380946 = T₄₃₃₁).

The spelling of 21664331 in words is "twenty-one million, six hundred sixty-four thousand, three hundred thirty-one".