81931 has 2 divisors, whose sum is σ = 81932. Its totient is φ = 81930.

The previous prime is 81929. The next prime is 81937. The reversal of 81931 is 13918.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81931 - 2¹ = 81929 is a prime.

It is a super-2 number, since 2×81931² = 13425377522, which contains 22 as substring.

Together with 81929, it forms a pair of twin primes.

81931 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (81937) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40965 + 40966.

It is an arithmetic number, because the mean of its divisors is an integer number (40966).

2⁸¹⁹³¹ is an apocalyptic number.

81931 is a deficient number, since it is larger than the sum of its proper divisors (1).

81931 is an equidigital number, since it uses as much as digits as its factorization.

81931 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 216, while the sum is 22.

The square root of 81931 is about 286.2359166841. The cubic root of 81931 is about 43.4326256974.

The spelling of 81931 in words is "eighty-one thousand, nine hundred thirty-one".