165551171155561 has 9 divisors (see below), whose sum is σ = 168310413772293. Its totient is φ = 162836445529920.

The previous prime is 165551171155537. The next prime is 165551171155589.

The square root of 165551171155561 is 12866669.

It is a perfect power (a square), and thus also a powerful number.

165551171155561 is nontrivially palindromic in base 10.

It can be written as a sum of positive squares in 4 ways, for example, as 145326183427161 + 20224987728400 = 12055131^2 + 4497220^2 .

It is not a de Polignac number, because 165551171155561 - 2⁵ = 165551171155529 is a prime.

It is a super-2 number, since 2×165551171155561² (a number of 29 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165551171155061) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 784761345 + ... + 784972273.

Almost surely, 2^{165551171155561} is an apocalyptic number.

165551171155561 is the 12866669-th square number.

165551171155561 is the 6433335-th centered octagonal number.

It is an amenable number.

165551171155561 is a deficient number, since it is larger than the sum of its proper divisors (2759242616732).

165551171155561 is an frugal number, since it uses more digits than its factorization.

165551171155561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 421980 (or 210990 counting only the distinct ones).

The product of its digits is 3937500, while the sum is 55.

The spelling of 165551171155561 in words is "one hundred sixty-five trillion, five hundred fifty-one billion, one hundred seventy-one million, one hundred fifty-five thousand, five hundred sixty-one".