81720442728 has 128 divisors (see below), whose sum is σ = 232125696000. Its totient is φ = 26626691520.

The previous prime is 81720442693. The next prime is 81720442801. The reversal of 81720442728 is 82724402718.

81720442728 is a `hidden beast` number, since 8 + 17 + 204 + 427 + 2 + 8 = 666.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 8715883 + ... + 8725253.

It is an arithmetic number, because the mean of its divisors is an integer number (1813482000).

Almost surely, 2^81720442728 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81720442728, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (116062848000).

81720442728 is an abundant number, since it is smaller than the sum of its proper divisors (150405253272).

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

81720442728 is a wasteful number, since it uses less digits than its factorization.

81720442728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10292 (or 10282 counting only the distinct ones).

The product of its (nonzero) digits is 401408, while the sum is 45.

The spelling of 81720442728 in words is "eighty-one billion, seven hundred twenty million, four hundred forty-two thousand, seven hundred twenty-eight".