165605521 has 4 divisors (see below), whose sum is σ = 165631600. Its totient is φ = 165579444.

The previous prime is 165605509. The next prime is 165605527. The reversal of 165605521 is 125506561.

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, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 125506561 = 23 ⋅5456807.

It is a cyclic number.

It is not a de Polignac number, because 165605521 - 2⁹ = 165605009 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165605527) 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, 3370 + ... + 18508.

It is an arithmetic number, because the mean of its divisors is an integer number (41407900).

Almost surely, 2^165605521 is an apocalyptic number.

It is an amenable number.

165605521 is a deficient number, since it is larger than the sum of its proper divisors (26079).

165605521 is a wasteful number, since it uses less digits than its factorization.

165605521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26078.

The product of its (nonzero) digits is 9000, while the sum is 31.

The square root of 165605521 is about 12868.7808668887. The cubic root of 165605521 is about 549.1507787005.

The spelling of 165605521 in words is "one hundred sixty-five million, six hundred five thousand, five hundred twenty-one".