161664638697081 has 135 divisors (see below), whose sum is σ = 264190988051991. Its totient is φ = 98474346711936.

The previous prime is 161664638697053. The next prime is 161664638697137. The reversal of 161664638697081 is 180796836466161.

The square root of 161664638697081 is 12714741.

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

161664638697081 is a `hidden beast` number, since 1 + 6 + 1 + 6 + 6 + 463 + 86 + 9 + 7 + 0 + 81 = 666.

It can be written as a sum of positive squares in 13 ways, for example, as 47149385304681 + 114515253392400 = 6866541^2 + 10701180^2 .

It is not a de Polignac number, because 161664638697081 - 2¹¹ = 161664638695033 is a prime.

It is a super-2 number, since 2×161664638697081² (a number of 29 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (161664638697181) by changing a digit.

It is a polite number, since it can be written in 134 ways as a sum of consecutive naturals, for example, 162151091475 + ... + 162151092471.

Almost surely, 2^{161664638697081} is an apocalyptic number.

161664638697081 is the 12714741-st square number.

161664638697081 is the 6357371-st centered octagonal number.

It is an amenable number.

161664638697081 is a deficient number, since it is larger than the sum of its proper divisors (102526349354910).

161664638697081 is an frugal number, since it uses more digits than its factorization.

161664638697081 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2250 (or 1122 counting only the distinct ones).

The product of its (nonzero) digits is 376233984, while the sum is 72.

The spelling of 161664638697081 in words is "one hundred sixty-one trillion, six hundred sixty-four billion, six hundred thirty-eight million, six hundred ninety-seven thousand, eighty-one".