21661630165 has 24 divisors (see below), whose sum is σ = 30373539840. Its totient is φ = 14787043488.

The previous prime is 21661630147. The next prime is 21661630169. The reversal of 21661630165 is 56103616612.

It is not a de Polignac number, because 21661630165 - 2²⁷ = 21527412437 is a prime.

It is a super-4 number, since 4×21661630165⁴ (a number of 42 digits) contains 4444 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21661630169) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 143605 + ... + 252874.

It is an arithmetic number, because the mean of its divisors is an integer number (1265564160).

Almost surely, 2^21661630165 is an apocalyptic number.

It is an amenable number.

21661630165 is a deficient number, since it is larger than the sum of its proper divisors (8711909675).

21661630165 is a wasteful number, since it uses less digits than its factorization.

21661630165 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 396721 (or 396714 counting only the distinct ones).

The product of its (nonzero) digits is 38880, while the sum is 37.

The spelling of 21661630165 in words is "twenty-one billion, six hundred sixty-one million, six hundred thirty thousand, one hundred sixty-five".