81661181 has 16 divisors (see below), whose sum is σ = 96056064. Its totient is φ = 67976064.

The previous prime is 81661159. The next prime is 81661189. The reversal of 81661181 is 18116618.

It is a cyclic number.

It is not a de Polignac number, because 81661181 - 2²² = 77466877 is a prime.

It is a super-2 number, since 2×81661181² = 13337096964629522, which contains 22 as substring.

It is a Smith number, since the sum of its digits (32) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

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 (81661189) 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, 37145 + ... + 39281.

It is an arithmetic number, because the mean of its divisors is an integer number (6003504).

Almost surely, 2^81661181 is an apocalyptic number.

It is an amenable number.

81661181 is a deficient number, since it is larger than the sum of its proper divisors (14394883).

81661181 is a wasteful number, since it uses less digits than its factorization.

81661181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2300.

The product of its digits is 2304, while the sum is 32.

The square root of 81661181 is about 9036.6576232587. The cubic root of 81661181 is about 433.8489514491.

Adding to 81661181 its reverse (18116618), we get a palindrome (99777799).

The spelling of 81661181 in words is "eighty-one million, six hundred sixty-one thousand, one hundred eighty-one".