81637181 has 4 divisors (see below), whose sum is σ = 81719100. Its totient is φ = 81555264.

The previous prime is 81637169. The next prime is 81637183. The reversal of 81637181 is 18173618.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 26357956 + 55279225 = 5134^2 + 7435^2 .

It is a cyclic number.

It is not a de Polignac number, because 81637181 - 2¹⁰ = 81636157 is a prime.

It is a super-2 number, since 2×81637181² = 13329258643253522, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81637183) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 39446 + ... + 41463.

It is an arithmetic number, because the mean of its divisors is an integer number (20429775).

Almost surely, 2^81637181 is an apocalyptic number.

It is an amenable number.

81637181 is a deficient number, since it is larger than the sum of its proper divisors (81919).

81637181 is a wasteful number, since it uses less digits than its factorization.

81637181 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 81918.

The product of its digits is 8064, while the sum is 35.

The square root of 81637181 is about 9035.3296010716. The cubic root of 81637181 is about 433.8064449406.

It can be divided in two parts, 81637 and 181, that added together give a palindrome (81818).

The spelling of 81637181 in words is "eighty-one million, six hundred thirty-seven thousand, one hundred eighty-one".