81373991 has 2 divisors, whose sum is σ = 81373992. Its totient is φ = 81373990.

The previous prime is 81373987. The next prime is 81373997. The reversal of 81373991 is 19937318.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81373991 - 2² = 81373987 is a prime.

It is a super-2 number, since 2×81373991² = 13243452822536162, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81373997) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40686995 + 40686996.

It is an arithmetic number, because the mean of its divisors is an integer number (40686996).

Almost surely, 2^81373991 is an apocalyptic number.

81373991 is a deficient number, since it is larger than the sum of its proper divisors (1).

81373991 is an equidigital number, since it uses as much as digits as its factorization.

81373991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 40824, while the sum is 41.

The square root of 81373991 is about 9020.7533499149. The cubic root of 81373991 is about 433.3397603912.

The spelling of 81373991 in words is "eighty-one million, three hundred seventy-three thousand, nine hundred ninety-one".