21664631221 has 8 divisors (see below), whose sum is σ = 22727347200. Its totient is φ = 20622959280.

The previous prime is 21664631179. The next prime is 21664631251. The reversal of 21664631221 is 12213646612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21664631221 - 2²⁷ = 21530413493 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664631251) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5258901 + ... + 5263018.

It is an arithmetic number, because the mean of its divisors is an integer number (2840918400).

Almost surely, 2^21664631221 is an apocalyptic number.

It is an amenable number.

21664631221 is a deficient number, since it is larger than the sum of its proper divisors (1062715979).

21664631221 is a wasteful number, since it uses less digits than its factorization.

21664631221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10522019.

The product of its digits is 20736, while the sum is 34.

The spelling of 21664631221 in words is "twenty-one billion, six hundred sixty-four million, six hundred thirty-one thousand, two hundred twenty-one".