165565561 has 6 divisors (see below), whose sum is σ = 192596730. Its totient is φ = 141913296.

The previous prime is 165565549. The next prime is 165565579.

165565561 is nontrivially palindromic in base 10.

It can be written as a sum of positive squares in only one way, i.e., 164994025 + 571536 = 12845^2 + 756^2 .

It is not a de Polignac number, because 165565561 - 2¹⁹ = 165041273 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165565501) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1689396 + ... + 1689493.

It is an arithmetic number, because the mean of its divisors is an integer number (32099455).

Almost surely, 2^165565561 is an apocalyptic number.

It is an amenable number.

165565561 is a deficient number, since it is larger than the sum of its proper divisors (27031169).

165565561 is an equidigital number, since it uses as much as digits as its factorization.

165565561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3378903 (or 3378896 counting only the distinct ones).

The product of its digits is 135000, while the sum is 40.

The square root of 165565561 is about 12867.2281785939. The cubic root of 165565561 is about 549.1066057965.

The spelling of 165565561 in words is "one hundred sixty-five million, five hundred sixty-five thousand, five hundred sixty-one".