81806 has 4 divisors (see below), whose sum is σ = 122712. Its totient is φ = 40902.

The previous prime is 81799. The next prime is 81817. The reversal of 81806 is 60818.

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

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 20450 + ... + 20453.

It is an arithmetic number, because the mean of its divisors is an integer number (30678).

2⁸¹⁸⁰⁶ is an apocalyptic number.

81806 is a deficient number, since it is larger than the sum of its proper divisors (40906).

81806 is a wasteful number, since it uses less digits than its factorization.

81806 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40905.

The product of its (nonzero) digits is 384, while the sum is 23.

The square root of 81806 is about 286.0174819832. The cubic root of 81806 is about 43.4105264449.

The spelling of 81806 in words is "eighty-one thousand, eight hundred six".