165666561 has 4 divisors (see below), whose sum is σ = 220888752. Its totient is φ = 110444372.

The previous prime is 165666551. The next prime is 165666577.

165666561 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 cyclic number.

It is not a de Polignac number, because 165666561 - 2⁷ = 165666433 is a prime.

It is not an unprimeable number, because it can be changed into a prime (165666521) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 27611091 + ... + 27611096.

It is an arithmetic number, because the mean of its divisors is an integer number (55222188).

Almost surely, 2^165666561 is an apocalyptic number.

It is an amenable number.

165666561 is a deficient number, since it is larger than the sum of its proper divisors (55222191).

165666561 is an equidigital number, since it uses as much as digits as its factorization.

165666561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55222190.

The product of its digits is 194400, while the sum is 42.

The square root of 165666561 is about 12871.1522794193. The cubic root of 165666561 is about 549.2182403121.

The spelling of 165666561 in words is "one hundred sixty-five million, six hundred sixty-six thousand, five hundred sixty-one".