81681537312 has 36 divisors (see below), whose sum is σ = 232281872550. Its totient is φ = 27227179008.

The previous prime is 81681537247. The next prime is 81681537317. The reversal of 81681537312 is 21373518618.

It is a happy number.

81681537312 is a `hidden beast` number, since 8 + 1 + 6 + 81 + 537 + 31 + 2 = 666.

It can be written as a sum of positive squares in only one way, i.e., 44387747856 + 37293789456 = 210684^2 + 193116^2 .

It is a tau number, because it is divible by the number of its divisors (36).

It is not an unprimeable number, because it can be changed into a prime (81681537317) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 141807937 + ... + 141808512.

Almost surely, 2^81681537312 is an apocalyptic number.

It is an amenable number.

81681537312 is an abundant number, since it is smaller than the sum of its proper divisors (150600335238).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81681537312 is a wasteful number, since it uses less digits than its factorization.

81681537312 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 283616465 (or 283616454 counting only the distinct ones).

The product of its digits is 241920, while the sum is 45.

The spelling of 81681537312 in words is "eighty-one billion, six hundred eighty-one million, five hundred thirty-seven thousand, three hundred twelve".