81900 has 108 divisors (see below), whose sum is σ = 315952. Its totient is φ = 17280.

The previous prime is 81899. The next prime is 81901. The reversal of 81900 is 918.

81900 = T₆₄ + T₆₅ + ... + T₉₀.

It is an interprime number because it is at equal distance from previous prime (81899) and next prime (81901).

It is a super-2 number, since 2×81900² = 13415220000, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is not an unprimeable number, because it can be changed into a prime (81901) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 6294 + ... + 6306.

2⁸¹⁹⁰⁰ 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 81900, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (157976).

81900 is an abundant number, since it is smaller than the sum of its proper divisors (234052).

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

81900 is a wasteful number, since it uses less digits than its factorization.

81900 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40 (or 30 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 18.

The square root of 81900 is about 286.1817604251. The cubic root of 81900 is about 43.4271471799.

Adding to 81900 its sum of digits (18), we get a palindrome (81918).

It can be divided in two parts, 81 and 900, that multiplied together give a square (72900 = 270²).

The spelling of 81900 in words is "eighty-one thousand, nine hundred".