165643921 has 12 divisors (see below), whose sum is σ = 170692060. Its totient is φ = 160729920.

The previous prime is 165643913. The next prime is 165643967. The reversal of 165643921 is 129346561.

It can be written as a sum of positive squares in 6 ways, for example, as 12503296 + 153140625 = 3536^2 + 12375^2 .

It is not a de Polignac number, because 165643921 - 2³ = 165643913 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165643991) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 305911 + ... + 306451.

Almost surely, 2^165643921 is an apocalyptic number.

It is an amenable number.

165643921 is a deficient number, since it is larger than the sum of its proper divisors (5048139).

165643921 is an equidigital number, since it uses as much as digits as its factorization.

165643921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 756 (or 703 counting only the distinct ones).

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

The square root of 165643921 is about 12870.2727632323. The cubic root of 165643921 is about 549.1932204422.

The spelling of 165643921 in words is "one hundred sixty-five million, six hundred forty-three thousand, nine hundred twenty-one".