81813 has 4 divisors (see below), whose sum is σ = 109088. Its totient is φ = 54540.

The previous prime is 81799. The next prime is 81817. The reversal of 81813 is 31818.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 81813 - 2⁶ = 81749 is a prime.

It is a D-number.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 81813.

It is a congruent number.

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

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13633 + ... + 13638.

It is an arithmetic number, because the mean of its divisors is an integer number (27272).

2⁸¹⁸¹³ is an apocalyptic number.

It is an amenable number.

81813 is a deficient number, since it is larger than the sum of its proper divisors (27275).

81813 is a wasteful number, since it uses less digits than its factorization.

81813 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27274.

The product of its digits is 192, while the sum is 21.

The square root of 81813 is about 286.0297187357. The cubic root of 81813 is about 43.4117645979.

The spelling of 81813 in words is "eighty-one thousand, eight hundred thirteen".