81911231 has 2 divisors, whose sum is σ = 81911232. Its totient is φ = 81911230.

The previous prime is 81911213. The next prime is 81911233. The reversal of 81911231 is 13211918.

Together with previous prime (81911213) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81911231 - 2²² = 77716927 is a prime.

It is a super-2 number, since 2×81911231² = 13418899527870722, which contains 22 as substring.

Together with 81911233, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 81911231.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81911233) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40955615 + 40955616.

It is an arithmetic number, because the mean of its divisors is an integer number (40955616).

Almost surely, 2^81911231 is an apocalyptic number.

81911231 is a deficient number, since it is larger than the sum of its proper divisors (1).

81911231 is an equidigital number, since it uses as much as digits as its factorization.

81911231 is an evil number, because the sum of its binary digits is even.

The product of its digits is 432, while the sum is 26.

The square root of 81911231 is about 9050.4823628357. The cubic root of 81911231 is about 434.2913215345.

The spelling of 81911231 in words is "eighty-one million, nine hundred eleven thousand, two hundred thirty-one".