81815 has 4 divisors (see below), whose sum is σ = 98184. Its totient is φ = 65448.

The previous prime is 81799. The next prime is 81817. The reversal of 81815 is 51818.

81815 = 37² + 38² + ... + 66².

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81815 - 2⁴ = 81799 is a prime.

It is a Duffinian number.

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 81815.

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 3 ways as a sum of consecutive naturals, for example, 8177 + ... + 8186.

It is an arithmetic number, because the mean of its divisors is an integer number (24546).

2⁸¹⁸¹⁵ is an apocalyptic number.

81815 is a deficient number, since it is larger than the sum of its proper divisors (16369).

81815 is a wasteful number, since it uses less digits than its factorization.

81815 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16368.

The product of its digits is 320, while the sum is 23.

The square root of 81815 is about 286.0332148545. The cubic root of 81815 is about 43.4121183429.

The spelling of 81815 in words is "eighty-one thousand, eight hundred fifteen".