21664823917 has 4 divisors (see below), whose sum is σ = 23634353376. Its totient is φ = 19695294460.

The previous prime is 21664823903. The next prime is 21664823923. The reversal of 21664823917 is 71932846612.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21664823917 - 2²³ = 21656435309 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 (21664893917) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 984764713 + ... + 984764734.

It is an arithmetic number, because the mean of its divisors is an integer number (5908588344).

Almost surely, 2^21664823917 is an apocalyptic number.

It is an amenable number.

21664823917 is a deficient number, since it is larger than the sum of its proper divisors (1969529459).

21664823917 is a wasteful number, since it uses less digits than its factorization.

21664823917 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1969529458.

The product of its digits is 870912, while the sum is 49.

The spelling of 21664823917 in words is "twenty-one billion, six hundred sixty-four million, eight hundred twenty-three thousand, nine hundred seventeen".