81999972 has 96 divisors (see below), whose sum is σ = 226800000. Its totient is φ = 25546752.

The previous prime is 81999971. The next prime is 81999989. The reversal of 81999972 is 27999918.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is not an unprimeable number, because it can be changed into a prime (81999971) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 182404 + ... + 182852.

It is an arithmetic number, because the mean of its divisors is an integer number (2362500).

Almost surely, 2^81999972 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 81999972, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (113400000).

81999972 is an abundant number, since it is smaller than the sum of its proper divisors (144800028).

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

81999972 is a wasteful number, since it uses less digits than its factorization.

81999972 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 570 (or 562 counting only the distinct ones).

The product of its digits is 734832, while the sum is 54.

The square root of 81999972 is about 9055.3835920959. The cubic root of 81999972 is about 434.4480991275.

Subtracting from 81999972 its sum of digits (54), we obtain a palindrome (81999918).

The spelling of 81999972 in words is "eighty-one million, nine hundred ninety-nine thousand, nine hundred seventy-two".