165511561 has 4 divisors (see below), whose sum is σ = 165538512. Its totient is φ = 165484612.

The previous prime is 165511537. The next prime is 165511571. The reversal of 165511561 is 165115561.

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 165511561 - 2¹³ = 165503369 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165511501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 726 + ... + 18208.

It is an arithmetic number, because the mean of its divisors is an integer number (41384628).

Almost surely, 2^165511561 is an apocalyptic number.

It is an amenable number.

165511561 is a deficient number, since it is larger than the sum of its proper divisors (26951).

165511561 is an equidigital number, since it uses as much as digits as its factorization.

165511561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26950.

The product of its digits is 4500, while the sum is 31.

The square root of 165511561 is about 12865.1296534469. The cubic root of 165511561 is about 549.0469013893.

The spelling of 165511561 in words is "one hundred sixty-five million, five hundred eleven thousand, five hundred sixty-one".