165215921 has 6 divisors (see below), whose sum is σ = 178902630. Its totient is φ = 152506848.

The previous prime is 165215909. The next prime is 165215927. The reversal of 165215921 is 129512561.

It can be written as a sum of positive squares in 3 ways, for example, as 3010225 + 162205696 = 1735^2 + 12736^2 .

It is a de Polignac number, because none of the positive numbers 2^k-165215921 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165215927) 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 5 ways as a sum of consecutive naturals, for example, 488636 + ... + 488973.

It is an arithmetic number, because the mean of its divisors is an integer number (29817105).

Almost surely, 2^165215921 is an apocalyptic number.

It is an amenable number.

165215921 is a deficient number, since it is larger than the sum of its proper divisors (13686709).

165215921 is an equidigital number, since it uses as much as digits as its factorization.

165215921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 977635 (or 977622 counting only the distinct ones).

The product of its digits is 5400, while the sum is 32.

The square root of 165215921 is about 12853.6345443614. The cubic root of 165215921 is about 548.7198004354.

The spelling of 165215921 in words is "one hundred sixty-five million, two hundred fifteen thousand, nine hundred twenty-one".