81994508728 has 64 divisors (see below), whose sum is σ = 170321760000. Its totient is φ = 37001432160.

The previous prime is 81994508663. The next prime is 81994508767. The reversal of 81994508728 is 82780549918.

It is a super-3 number, since 3×81994508728³ (a number of 34 digits) contains 333 as substring.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1452373 + ... + 1507771.

It is an arithmetic number, because the mean of its divisors is an integer number (2661277500).

Almost surely, 2^81994508728 is an apocalyptic number.

81994508728 is a gapful number since it is divisible by the number (88) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81994508728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (85160880000).

81994508728 is an abundant number, since it is smaller than the sum of its proper divisors (88327251272).

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

81994508728 is a wasteful number, since it uses less digits than its factorization.

81994508728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 55577 (or 55551 counting only the distinct ones).

The product of its (nonzero) digits is 11612160, while the sum is 61.

The spelling of 81994508728 in words is "eighty-one billion, nine hundred ninety-four million, five hundred eight thousand, seven hundred twenty-eight".