165221521 has 4 divisors (see below), whose sum is σ = 174940452. Its totient is φ = 155502592.

The previous prime is 165221519. The next prime is 165221533. The reversal of 165221521 is 125122561.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 125122561 = 43 ⋅2909827.

It can be written as a sum of positive squares in 2 ways, for example, as 55726225 + 109495296 = 7465^2 + 10464^2 .

It is a cyclic number.

It is not a de Polignac number, because 165221521 - 2¹ = 165221519 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165221501) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4859440 + ... + 4859473.

It is an arithmetic number, because the mean of its divisors is an integer number (43735113).

Almost surely, 2^165221521 is an apocalyptic number.

It is an amenable number.

165221521 is a deficient number, since it is larger than the sum of its proper divisors (9718931).

165221521 is an equidigital number, since it uses as much as digits as its factorization.

165221521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9718930.

The product of its digits is 1200, while the sum is 25.

The square root of 165221521 is about 12853.8523797343. The cubic root of 165221521 is about 548.7259999916.

The spelling of 165221521 in words is "one hundred sixty-five million, two hundred twenty-one thousand, five hundred twenty-one".