166165561661 has 16 divisors (see below), whose sum is σ = 185034103488. Its totient is φ = 147945379200.

The previous prime is 166165561613. The next prime is 166165561673.

166165561661 is nontrivially palindromic in base 10.

It is a cyclic number.

It is not a de Polignac number, because 166165561661 - 2²⁶ = 166098452797 is a prime.

It is a super-2 number, since 2×166165561661² (a number of 23 digits) contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (166165561361) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 375071 + ... + 687756.

It is an arithmetic number, because the mean of its divisors is an integer number (11564631468).

Almost surely, 2^166165561661 is an apocalyptic number.

166165561661 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

166165561661 is a deficient number, since it is larger than the sum of its proper divisors (18868541827).

166165561661 is a wasteful number, since it uses less digits than its factorization.

166165561661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1063132.

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

The spelling of 166165561661 in words is "one hundred sixty-six billion, one hundred sixty-five million, five hundred sixty-one thousand, six hundred sixty-one".