81331973 has 2 divisors, whose sum is σ = 81331974. Its totient is φ = 81331972.

The previous prime is 81331919. The next prime is 81331981. The reversal of 81331973 is 37913318.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 66945124 + 14386849 = 8182^2 + 3793^2 .

It is a cyclic number.

It is not a de Polignac number, because 81331973 - 2⁸ = 81331717 is a prime.

It is a super-2 number, since 2×81331973² = 13229779664145458, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81331273) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40665986 + 40665987.

It is an arithmetic number, because the mean of its divisors is an integer number (40665987).

Almost surely, 2^81331973 is an apocalyptic number.

It is an amenable number.

81331973 is a deficient number, since it is larger than the sum of its proper divisors (1).

81331973 is an equidigital number, since it uses as much as digits as its factorization.

81331973 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 13608, while the sum is 35.

The square root of 81331973 is about 9018.4240862803. The cubic root of 81331973 is about 433.2651615967.

The spelling of 81331973 in words is "eighty-one million, three hundred thirty-one thousand, nine hundred seventy-three".