81800 has 24 divisors (see below), whose sum is σ = 190650. Its totient is φ = 32640.

The previous prime is 81799. The next prime is 81817. The reversal of 81800 is 818.

It is a happy number.

It can be written as a sum of positive squares in 3 ways, for example, as 75076 + 6724 = 274^2 + 82^2 .

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 5 + ... + 404.

2⁸¹⁸⁰⁰ 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 81800, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (95325).

81800 is an abundant number, since it is smaller than the sum of its proper divisors (108850).

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

81800 is a wasteful number, since it uses less digits than its factorization.

81800 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 425 (or 416 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 17.

The square root of 81800 is about 286.0069929215. The cubic root of 81800 is about 43.4094651148.

Multiplying 81800 by its reverse (818), we get a square (66912400 = 8180²).

81800 divided by its reverse (818) gives a square (100 = 10²).

It can be divided in two parts, 8 and 1800, that multiplied together give a square (14400 = 120²).

The spelling of 81800 in words is "eighty-one thousand, eight hundred".