Multipling 81920 by its sum of digits (20), we get a square (1638400 = 12802).
81920 divided by its sum of digits (20) gives a 12-th power (4096 = 212).
It is an Ulam number.
It is a nialpdrome in base 4.
It is a zygodrome in base 4.
It is a congruent number.
It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 81920.
In principle, a polygon with 81920 sides can be constructed with ruler and compass.
81920 is a Friedman number, since it can be written as 80*2^(9+1), using all its digits and the basic arithmetic operations.
281920 is an apocalyptic number.
81920 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 81920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (98301).
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
81920 is an frugal number, since it uses more digits than its factorization.
81920 is an evil number, because the sum of its binary digits is even.
The square root of 81920 is about 286.2167011200. The cubic root of 81920 is about 43.4306818655.
The spelling of 81920 in words is "eighty-one thousand, nine hundred twenty".