205781 has 6 divisors (see below), whose sum is σ = 215670. Its totient is φ = 196328.

The previous prime is 205763. The next prime is 205783. The reversal of 205781 is 187502.

It can be written as a sum of positive squares in only one way, i.e., 152881 + 52900 = 391^2 + 230^2 .

It is a de Polignac number, because none of the positive numbers 2^k-205781 is a prime.

It is a super-2 number, since 2×205781² = 84691639922, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (23).

It is an Ulam number.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 205781.

It is not an unprimeable number, because it can be changed into a prime (205783) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 335 + ... + 723.

It is an arithmetic number, because the mean of its divisors is an integer number (35945).

2²⁰⁵⁷⁸¹ is an apocalyptic number.

It is an amenable number.

205781 is a deficient number, since it is larger than the sum of its proper divisors (9889).

205781 is an equidigital number, since it uses as much as digits as its factorization.

205781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 435 (or 412 counting only the distinct ones).

The product of its (nonzero) digits is 560, while the sum is 23.

The square root of 205781 is about 453.6309072363. The cubic root of 205781 is about 59.0384695968.

The spelling of 205781 in words is "two hundred five thousand, seven hundred eighty-one".