81905 has 4 divisors (see below), whose sum is σ = 98292. Its totient is φ = 65520.

The previous prime is 81901. The next prime is 81919. The reversal of 81905 is 50918.

81905 is nontrivially palindromic in base 4.

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

It can be written as a sum of positive squares in 2 ways, for example, as 8464 + 73441 = 92^2 + 271^2 .

It is not a de Polignac number, because 81905 - 2² = 81901 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81901) 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, 8186 + ... + 8195.

It is an arithmetic number, because the mean of its divisors is an integer number (24573).

2⁸¹⁹⁰⁵ is an apocalyptic number.

It is an amenable number.

81905 is a deficient number, since it is larger than the sum of its proper divisors (16387).

81905 is a wasteful number, since it uses less digits than its factorization.

81905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16386.

The product of its (nonzero) digits is 360, while the sum is 23.

The square root of 81905 is about 286.1904959987. The cubic root of 81905 is about 43.4280309053.

The spelling of 81905 in words is "eighty-one thousand, nine hundred five".