81537719138 has 18 divisors (see below), whose sum is σ = 129094714251. Its totient is φ = 38619495684.

The previous prime is 81537719063. The next prime is 81537719149. The reversal of 81537719138 is 83191773518.

It can be written as a sum of positive squares in only one way, i.e., 40768859569 + 40768859569 = 201913^2 + 201913^2 .

It is an ABA number since it can be written as A⋅B^A, here for A=2, B=201913.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81537719138.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 7667381 + ... + 7678007.

Almost surely, 2^81537719138 is an apocalyptic number.

81537719138 is a deficient number, since it is larger than the sum of its proper divisors (47556995113).

81537719138 is an frugal number, since it uses more digits than its factorization.

81537719138 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21294 (or 10648 counting only the distinct ones).

The product of its digits is 1270080, while the sum is 53.

The spelling of 81537719138 in words is "eighty-one billion, five hundred thirty-seven million, seven hundred nineteen thousand, one hundred thirty-eight".