205409 has 6 divisors (see below), whose sum is σ = 217170. Its totient is φ = 194256.

The previous prime is 205399. The next prime is 205417. The reversal of 205409 is 904502.

It can be written as a sum of positive squares in only one way, i.e., 144400 + 61009 = 380^2 + 247^2 .

It is a de Polignac number, because none of the positive numbers 2^k-205409 is a prime.

It is an Ulam number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (202409) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 77 + ... + 645.

It is an arithmetic number, because the mean of its divisors is an integer number (36195).

2²⁰⁵⁴⁰⁹ is an apocalyptic number.

It is an amenable number.

205409 is a deficient number, since it is larger than the sum of its proper divisors (11761).

205409 is an equidigital number, since it uses as much as digits as its factorization.

205409 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 607 (or 588 counting only the distinct ones).

The product of its (nonzero) digits is 360, while the sum is 20.

The square root of 205409 is about 453.2206967913. The cubic root of 205409 is about 59.0028725979.

It can be divided in two parts, 205 and 409, that multiplied together give a triangular number (83845 = T₄₀₉).

The spelling of 205409 in words is "two hundred five thousand, four hundred nine".