81607993 has 2 divisors, whose sum is σ = 81607994. Its totient is φ = 81607992.

The previous prime is 81607991. The next prime is 81608003. The reversal of 81607993 is 39970618.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 61653904 + 19954089 = 7852^2 + 4467^2 .

It is a cyclic number.

It is not a de Polignac number, because 81607993 - 2¹ = 81607991 is a prime.

Together with 81607991, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (81607991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40803996 + 40803997.

It is an arithmetic number, because the mean of its divisors is an integer number (40803997).

Almost surely, 2^81607993 is an apocalyptic number.

It is an amenable number.

81607993 is a deficient number, since it is larger than the sum of its proper divisors (1).

81607993 is an equidigital number, since it uses as much as digits as its factorization.

81607993 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 81648, while the sum is 43.

The square root of 81607993 is about 9033.7142416616. The cubic root of 81607993 is about 433.7547387136.

Subtracting from 81607993 its reverse (39970618), we obtain a triangular number (41637375 = T₉₁₂₅).

The spelling of 81607993 in words is "eighty-one million, six hundred seven thousand, nine hundred ninety-three".