81810 has 40 divisors (see below), whose sum is σ = 222156. Its totient is φ = 21600.

The previous prime is 81799. The next prime is 81817. The reversal of 81810 is 1818.

It is a happy number.

81810 is a nontrivial binomial coefficient, being equal to C(405, 2).

It can be written as a sum of positive squares in 2 ways, for example, as 77841 + 3969 = 279^2 + 63^2 .

It is a super-2 number, since 2×81810² = 13385752200, which contains 22 as substring.

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

It is an Ulam number.

It is an alternating number because its digits alternate between even and odd.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81817) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 760 + ... + 860.

2⁸¹⁸¹⁰ is an apocalyptic number.

81810 is the 404-th triangular number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81810, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (111078).

81810 is an abundant number, since it is smaller than the sum of its proper divisors (140346).

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

81810 is a wasteful number, since it uses less digits than its factorization.

81810 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 120 (or 111 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 18.

The square root of 81810 is about 286.0244744773. The cubic root of 81810 is about 43.4112339696.

81810 divided by its reverse (1818) gives a triangular number (45 = T₉).

It can be divided in two parts, 818 and 10, that added together give a palindrome (828).

The spelling of 81810 in words is "eighty-one thousand, eight hundred ten".