81131693 has 2 divisors, whose sum is σ = 81131694. Its totient is φ = 81131692.

The previous prime is 81131671. The next prime is 81131719. The reversal of 81131693 is 39613118.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 77757124 + 3374569 = 8818^2 + 1837^2 .

It is a cyclic number.

It is not a de Polignac number, because 81131693 - 2⁸ = 81131437 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81131623) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40565846 + 40565847.

It is an arithmetic number, because the mean of its divisors is an integer number (40565847).

Almost surely, 2^81131693 is an apocalyptic number.

It is an amenable number.

81131693 is a deficient number, since it is larger than the sum of its proper divisors (1).

81131693 is an equidigital number, since it uses as much as digits as its factorization.

81131693 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3888, while the sum is 32.

The square root of 81131693 is about 9007.3133064194. The cubic root of 81131693 is about 432.9092307606.

The spelling of 81131693 in words is "eighty-one million, one hundred thirty-one thousand, six hundred ninety-three".