165661166561 has 4 divisors (see below), whose sum is σ = 180721272624. Its totient is φ = 150601060500.

The previous prime is 165661166549. The next prime is 165661166579.

165661166561 is nontrivially palindromic in base 10.

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 de Polignac number, because none of the positive numbers 2^k-165661166561 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165661166761) 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, 7530053015 + ... + 7530053036.

It is an arithmetic number, because the mean of its divisors is an integer number (45180318156).

Almost surely, 2^165661166561 is an apocalyptic number.

165661166561 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

165661166561 is a deficient number, since it is larger than the sum of its proper divisors (15060106063).

165661166561 is a wasteful number, since it uses less digits than its factorization.

165661166561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15060106062.

The product of its digits is 1166400, while the sum is 50.

The spelling of 165661166561 in words is "one hundred sixty-five billion, six hundred sixty-one million, one hundred sixty-six thousand, five hundred sixty-one".