21664631 has 4 divisors (see below), whose sum is σ = 21675072. Its totient is φ = 21654192.

The previous prime is 21664609. The next prime is 21664637. The reversal of 21664631 is 13646612.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21664631 is a prime.

It is a super-2 number, since 2×21664631² = 938712472732322, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21664594 and 21664603.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664637) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 935 + ... + 6648.

It is an arithmetic number, because the mean of its divisors is an integer number (5418768).

Almost surely, 2^21664631 is an apocalyptic number.

21664631 is a deficient number, since it is larger than the sum of its proper divisors (10441).

21664631 is an equidigital number, since it uses as much as digits as its factorization.

21664631 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10440.

The product of its digits is 5184, while the sum is 29.

The square root of 21664631 is about 4654.5280104432. The cubic root of 21664631 is about 278.7728224391.

The spelling of 21664631 in words is "twenty-one million, six hundred sixty-four thousand, six hundred thirty-one".