205909 has 4 divisors (see below), whose sum is σ = 224640. Its totient is φ = 187180.

The previous prime is 205883. The next prime is 205913. The reversal of 205909 is 909502.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 205909 - 2⁹ = 205397 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (205949) 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, 9349 + ... + 9370.

It is an arithmetic number, because the mean of its divisors is an integer number (56160).

2²⁰⁵⁹⁰⁹ is an apocalyptic number.

It is an amenable number.

205909 is a deficient number, since it is larger than the sum of its proper divisors (18731).

205909 is a wasteful number, since it uses less digits than its factorization.

205909 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18730.

The product of its (nonzero) digits is 810, while the sum is 25.

The square root of 205909 is about 453.7719691651. The cubic root of 205909 is about 59.0507081057.

It can be divided in two parts, 20 and 5909, that added together give a square (5929 = 77²).

The spelling of 205909 in words is "two hundred five thousand, nine hundred nine".