81391693 has 2 divisors, whose sum is σ = 81391694. Its totient is φ = 81391692.

The previous prime is 81391679. The next prime is 81391703. The reversal of 81391693 is 39619318.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 49378729 + 32012964 = 7027^2 + 5658^2 .

It is a cyclic number.

It is not a de Polignac number, because 81391693 - 2²⁵ = 47837261 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81391493) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40695846 + 40695847.

It is an arithmetic number, because the mean of its divisors is an integer number (40695847).

Almost surely, 2^81391693 is an apocalyptic number.

It is an amenable number.

81391693 is a deficient number, since it is larger than the sum of its proper divisors (1).

81391693 is an equidigital number, since it uses as much as digits as its factorization.

81391693 is an evil number, because the sum of its binary digits is even.

The product of its digits is 34992, while the sum is 40.

The square root of 81391693 is about 9021.7344784692. The cubic root of 81391693 is about 433.3711808494.

The spelling of 81391693 in words is "eighty-one million, three hundred ninety-one thousand, six hundred ninety-three".