161731861281 has 9 divisors (see below), whose sum is σ = 233614431219. Its totient is φ = 107820436536.

The previous prime is 161731861273. The next prime is 161731861297. The reversal of 161731861281 is 182168137161.

The square root of 161731861281 is 402159.

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

161731861281 is a `hidden beast` number, since 1 + 6 + 17 + 3 + 18 + 612 + 8 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 21043854225 + 140688007056 = 145065^2 + 375084^2 .

It is a tau number, because it is divible by the number of its divisors (9).

It is not a de Polignac number, because 161731861281 - 2³ = 161731861273 is a prime.

It is a super-2 number, since 2×161731861281² (a number of 23 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (161731861261) 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, 1139451 + ... + 1273503.

Almost surely, 2^161731861281 is an apocalyptic number.

161731861281 is the 402159-th square number.

161731861281 is the 201080-th centered octagonal number.

It is an amenable number.

161731861281 is a deficient number, since it is larger than the sum of its proper divisors (71882569938).

161731861281 is an frugal number, since it uses more digits than its factorization.

161731861281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 268112 (or 134056 counting only the distinct ones).

The product of its digits is 96768, while the sum is 45.

The spelling of 161731861281 in words is "one hundred sixty-one billion, seven hundred thirty-one million, eight hundred sixty-one thousand, two hundred eighty-one".