81891976717 has 4 divisors (see below), whose sum is σ = 86709151836. Its totient is φ = 77074801600.

The previous prime is 81891976709. The next prime is 81891976723. The reversal of 81891976717 is 71767919818.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 28080040041 + 53811936676 = 167571^2 + 231974^2 .

It is a cyclic number.

It is not a de Polignac number, because 81891976717 - 2³ = 81891976709 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 (81891976417) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2408587534 + ... + 2408587567.

It is an arithmetic number, because the mean of its divisors is an integer number (21677287959).

Almost surely, 2^81891976717 is an apocalyptic number.

It is an amenable number.

81891976717 is a deficient number, since it is larger than the sum of its proper divisors (4817175119).

81891976717 is a wasteful number, since it uses less digits than its factorization.

81891976717 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4817175118.

The product of its digits is 10668672, while the sum is 64.

The spelling of 81891976717 in words is "eighty-one billion, eight hundred ninety-one million, nine hundred seventy-six thousand, seven hundred seventeen".