165621521 has 12 divisors (see below), whose sum is σ = 182030832. Its totient is φ = 150589296.

The previous prime is 165621457. The next prime is 165621553. The reversal of 165621521 is 125126561.

It is a happy number.

It is not a de Polignac number, because 165621521 - 2⁶ = 165621457 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165621121) 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, 4010 + ... + 18636.

It is an arithmetic number, because the mean of its divisors is an integer number (15169236).

Almost surely, 2^165621521 is an apocalyptic number.

It is an amenable number.

165621521 is a deficient number, since it is larger than the sum of its proper divisors (16409311).

165621521 is a wasteful number, since it uses less digits than its factorization.

165621521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14720 (or 14707 counting only the distinct ones).

The product of its digits is 3600, while the sum is 29.

The square root of 165621521 is about 12869.4025113833. The cubic root of 165621521 is about 549.1684635568.

The spelling of 165621521 in words is "one hundred sixty-five million, six hundred twenty-one thousand, five hundred twenty-one".