81115920 has 120 divisors (see below), whose sum is σ = 275100696. Its totient is φ = 21417984.

The previous prime is 81115913. The next prime is 81115939. The reversal of 81115920 is 2951118.

It can be written as a sum of positive squares in 4 ways, for example, as 3111696 + 78004224 = 1764^2 + 8832^2 .

It is a tau number, because it is divible by the number of its divisors (120).

It is an unprimeable number.

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 23 ways as a sum of consecutive naturals, for example, 80862 + ... + 81858.

Almost surely, 2^81115920 is an apocalyptic number.

81115920 is a gapful number since it is divisible by the number (80) 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 81115920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (137550348).

81115920 is an abundant number, since it is smaller than the sum of its proper divisors (193984776).

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

81115920 is a wasteful number, since it uses less digits than its factorization.

81115920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1129 (or 1120 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 27.

The square root of 81115920 is about 9006.4376975583. The cubic root of 81115920 is about 432.8811746476.

The spelling of 81115920 in words is "eighty-one million, one hundred fifteen thousand, nine hundred twenty".