81115691728 has 40 divisors (see below), whose sum is σ = 158063934600. Its totient is φ = 40325505024.

The previous prime is 81115691719. The next prime is 81115691729. The reversal of 81115691728 is 82719651118.

It can be written as a sum of positive squares in 4 ways, for example, as 10884331584 + 70231360144 = 104328^2 + 265012^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81115691729) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2627808 + ... + 2658496.

It is an arithmetic number, because the mean of its divisors is an integer number (3951598365).

Almost surely, 2^81115691728 is an apocalyptic number.

It is an amenable number.

81115691728 is a deficient number, since it is larger than the sum of its proper divisors (76948242872).

81115691728 is a wasteful number, since it uses less digits than its factorization.

81115691728 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 31639 (or 31633 counting only the distinct ones).

The product of its digits is 241920, while the sum is 49.

The spelling of 81115691728 in words is "eighty-one billion, one hundred fifteen million, six hundred ninety-one thousand, seven hundred twenty-eight".