81991168281 has 27 divisors (see below), whose sum is σ = 130191983103. Its totient is φ = 49685890320.

The previous prime is 81991168271. The next prime is 81991168289. The reversal of 81991168281 is 18286119918.

The square root of 81991168281 is 286341.

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

It can be written as a sum of positive squares in only one way, i.e., 21516489225 + 60474679056 = 146685^2 + 245916^2 .

It is not a de Polignac number, because 81991168281 - 2¹¹ = 81991166233 is a prime.

It is a super-2 number, since 2×81991168281² (a number of 23 digits) contains 22 as substring.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81991168289) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 9444915 + ... + 9453591.

Almost surely, 2^81991168281 is an apocalyptic number.

81991168281 is the 286341-st square number.

81991168281 is the 143171-st centered octagonal number.

It is an amenable number.

81991168281 is a deficient number, since it is larger than the sum of its proper divisors (48200814822).

81991168281 is an frugal number, since it uses more digits than its factorization.

81991168281 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17382 (or 8691 counting only the distinct ones).

The product of its digits is 497664, while the sum is 54.

The spelling of 81991168281 in words is "eighty-one billion, nine hundred ninety-one million, one hundred sixty-eight thousand, two hundred eighty-one".