205813509 has 16 divisors (see below), whose sum is σ = 316975680. Its totient is φ = 117397760.

The previous prime is 205813477. The next prime is 205813511. The reversal of 205813509 is 905318502.

It is a cyclic number.

It is not a de Polignac number, because 205813509 - 2⁵ = 205813477 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 205813509.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (205813519) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 182874 + ... + 183995.

It is an arithmetic number, because the mean of its divisors is an integer number (19810980).

Almost surely, 2^205813509 is an apocalyptic number.

It is an amenable number.

205813509 is a deficient number, since it is larger than the sum of its proper divisors (111162171).

205813509 is a wasteful number, since it uses less digits than its factorization.

205813509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 366900.

The product of its (nonzero) digits is 10800, while the sum is 33.

The square root of 205813509 is about 14346.2019015487. The cubic root of 205813509 is about 590.4157837187.

It can be divided in two parts, 20581 and 3509, that added together give a triangular number (24090 = T₂₁₉).

The spelling of 205813509 in words is "two hundred five million, eight hundred thirteen thousand, five hundred nine".