81157231 has 4 divisors (see below), whose sum is σ = 82069200. Its totient is φ = 80245264.

The previous prime is 81157229. The next prime is 81157261. The reversal of 81157231 is 13275118.

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

It is a cyclic number.

It is not a de Polignac number, because 81157231 - 2¹ = 81157229 is a prime.

It is a super-2 number, since 2×81157231² = 13172992287174722, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81157231.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81157261) 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, 455851 + ... + 456028.

It is an arithmetic number, because the mean of its divisors is an integer number (20517300).

Almost surely, 2^81157231 is an apocalyptic number.

81157231 is a deficient number, since it is larger than the sum of its proper divisors (911969).

81157231 is an equidigital number, since it uses as much as digits as its factorization.

81157231 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 911968.

The product of its digits is 1680, while the sum is 28.

The square root of 81157231 is about 9008.7308207094. The cubic root of 81157231 is about 432.9546485898.

The spelling of 81157231 in words is "eighty-one million, one hundred fifty-seven thousand, two hundred thirty-one".