81691974791 has 12 divisors (see below), whose sum is σ = 95754863160. Its totient is φ = 69487170480.

The previous prime is 81691974769. The next prime is 81691974797. The reversal of 81691974791 is 19747919618.

It is a de Polignac number, because none of the positive numbers 2^k-81691974791 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81691974797) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 6356876 + ... + 6369713.

It is an arithmetic number, because the mean of its divisors is an integer number (7979571930).

Almost surely, 2^81691974791 is an apocalyptic number.

81691974791 is a deficient number, since it is larger than the sum of its proper divisors (14062888369).

81691974791 is a wasteful number, since it uses less digits than its factorization.

81691974791 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 12726734 (or 12726727 counting only the distinct ones).

The product of its digits is 6858432, while the sum is 62.

The spelling of 81691974791 in words is "eighty-one billion, six hundred ninety-one million, nine hundred seventy-four thousand, seven hundred ninety-one".