165399521 has 4 divisors (see below), whose sum is σ = 189028032. Its totient is φ = 141771012.

The previous prime is 165399517. The next prime is 165399547. The reversal of 165399521 is 125993561.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 165399521 - 2² = 165399517 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165399551) 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 3 ways as a sum of consecutive naturals, for example, 11814245 + ... + 11814258.

It is an arithmetic number, because the mean of its divisors is an integer number (47257008).

Almost surely, 2^165399521 is an apocalyptic number.

It is an amenable number.

165399521 is a deficient number, since it is larger than the sum of its proper divisors (23628511).

165399521 is an equidigital number, since it uses as much as digits as its factorization.

165399521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23628510.

The product of its digits is 72900, while the sum is 41.

The square root of 165399521 is about 12860.7745101141. The cubic root of 165399521 is about 548.9229843646.

The spelling of 165399521 in words is "one hundred sixty-five million, three hundred ninety-nine thousand, five hundred twenty-one".