205805 has 4 divisors (see below), whose sum is σ = 246972. Its totient is φ = 164640.

The previous prime is 205783. The next prime is 205817. The reversal of 205805 is 508502.

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 111556 + 94249 = 334^2 + 307^2 .

It is not a de Polignac number, because 205805 - 2⁸ = 205549 is a prime.

It is a Duffinian number.

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 in 3 ways as a sum of consecutive naturals, for example, 20576 + ... + 20585.

It is an arithmetic number, because the mean of its divisors is an integer number (61743).

2²⁰⁵⁸⁰⁵ is an apocalyptic number.

It is an amenable number.

205805 is a deficient number, since it is larger than the sum of its proper divisors (41167).

205805 is an equidigital number, since it uses as much as digits as its factorization.

205805 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41166.

The product of its (nonzero) digits is 400, while the sum is 20.

The square root of 205805 is about 453.6573596890. The cubic root of 205805 is about 59.0407647037.

It can be divided in two parts, 205 and 805, that multiplied together give a triangular number (165025 = T₅₇₄).

The spelling of 205805 in words is "two hundred five thousand, eight hundred five".