165983722921 has 9 divisors (see below), whose sum is σ = 169196591991. Its totient is φ = 162830769192.

The previous prime is 165983722909. The next prime is 165983722943. The reversal of 165983722921 is 129227389561.

The square root of 165983722921 is 407411.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 119657187225 + 46326535696 = 345915^2 + 215236^2 .

It is not a de Polignac number, because 165983722921 - 2¹⁵ = 165983690153 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165983722951) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 21588940 + ... + 21596626.

Almost surely, 2^165983722921 is an apocalyptic number.

165983722921 is the 407411-st square number.

165983722921 is the 203706-th centered octagonal number.

It is an amenable number.

165983722921 is a deficient number, since it is larger than the sum of its proper divisors (3212869070).

165983722921 is an frugal number, since it uses more digits than its factorization.

165983722921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15480 (or 7740 counting only the distinct ones).

The product of its digits is 3265920, while the sum is 55.

The spelling of 165983722921 in words is "one hundred sixty-five billion, nine hundred eighty-three million, seven hundred twenty-two thousand, nine hundred twenty-one".