165121561 has 12 divisors (see below), whose sum is σ = 192175956. Its totient is φ = 141278720.

The previous prime is 165121549. The next prime is 165121597.

It is a happy number.

165121561 is nontrivially palindromic in base 10.

It can be written as a sum of positive squares in 2 ways, for example, as 88454025 + 76667536 = 9405^2 + 8756^2 .

It is not a de Polignac number, because 165121561 - 2⁵ = 165121529 is a prime.

It is a super-3 number, since 3×165121561³ (a number of 26 digits) contains 333 as substring.

It is not an unprimeable number, because it can be changed into a prime (165121261) 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, 38080 + ... + 42193.

It is an arithmetic number, because the mean of its divisors is an integer number (16014663).

Almost surely, 2^165121561 is an apocalyptic number.

165121561 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

165121561 is a deficient number, since it is larger than the sum of its proper divisors (27054395).

165121561 is a wasteful number, since it uses less digits than its factorization.

165121561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 80312 (or 80301 counting only the distinct ones).

The product of its digits is 1800, while the sum is 28.

The square root of 165121561 is about 12849.9634629831. The cubic root of 165121561 is about 548.6153168392.

The spelling of 165121561 in words is "one hundred sixty-five million, one hundred twenty-one thousand, five hundred sixty-one".