81696521391 has 8 divisors (see below), whose sum is σ = 108944977584. Its totient is φ = 54456206400.

The previous prime is 81696521369. The next prime is 81696521407. The reversal of 81696521391 is 19312569618.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81696521391 - 2⁶ = 81696521327 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81696521791) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2011846 + ... + 2052051.

It is an arithmetic number, because the mean of its divisors is an integer number (13618122198).

Almost surely, 2^81696521391 is an apocalyptic number.

81696521391 is a deficient number, since it is larger than the sum of its proper divisors (27248456193).

81696521391 is a wasteful number, since it uses less digits than its factorization.

81696521391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4070601.

The product of its digits is 699840, while the sum is 51.

The spelling of 81696521391 in words is "eighty-one billion, six hundred ninety-six million, five hundred twenty-one thousand, three hundred ninety-one".