81994508729 has 6 divisors (see below), whose sum is σ = 95381367354. Its totient is φ = 70281007440.

The previous prime is 81994508663. The next prime is 81994508767. The reversal of 81994508729 is 92780549918.

It can be written as a sum of positive squares in only one way, i.e., 78541183504 + 3453325225 = 280252^2 + 58765^2 .

It is not a de Polignac number, because 81994508729 - 2³⁶ = 13275031993 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81994508129) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 836678612 + ... + 836678709.

It is an arithmetic number, because the mean of its divisors is an integer number (15896894559).

Almost surely, 2^81994508729 is an apocalyptic number.

It is an amenable number.

81994508729 is a deficient number, since it is larger than the sum of its proper divisors (13386858625).

81994508729 is a wasteful number, since it uses less digits than its factorization.

81994508729 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1673357335 (or 1673357328 counting only the distinct ones).

The product of its (nonzero) digits is 13063680, while the sum is 62.

The spelling of 81994508729 in words is "eighty-one billion, nine hundred ninety-four million, five hundred eight thousand, seven hundred twenty-nine".