81811 has 4 divisors (see below), whose sum is σ = 85392. Its totient is φ = 78232.

The previous prime is 81799. The next prime is 81817. The reversal of 81811 is 11818.

81811 is nontrivially palindromic in base 15.

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 81811 - 2⁹ = 81299 is a prime.

It is a pancake number, because a pancake can be divided into 81811 parts by 404 straight cuts.

It is a Duffinian number.

81811 is a lucky 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, 1756 + ... + 1801.

It is an arithmetic number, because the mean of its divisors is an integer number (21348).

2⁸¹⁸¹¹ is an apocalyptic number.

81811 is a deficient number, since it is larger than the sum of its proper divisors (3581).

81811 is a wasteful number, since it uses less digits than its factorization.

81811 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3580.

The product of its digits is 64, while the sum is 19.

The square root of 81811 is about 286.0262225741. The cubic root of 81811 is about 43.4114108471.

It can be divided in two parts, 818 and 11, that multiplied together give a palindrome (8998).

The spelling of 81811 in words is "eighty-one thousand, eight hundred eleven".