181809 has 6 divisors (see below), whose sum is σ = 262626. Its totient is φ = 121200.

The previous prime is 181789. The next prime is 181813. The reversal of 181809 is 908181.

It can be written as a sum of positive squares in only one way, i.e., 91809 + 90000 = 303^2 + 300^2 .

It is not a de Polignac number, because 181809 - 2⁵ = 181777 is a prime.

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 181809.

It is not an unprimeable number, because it can be changed into a prime (181889) 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, 10092 + ... + 10109.

It is an arithmetic number, because the mean of its divisors is an integer number (43771).

2¹⁸¹⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

181809 is a deficient number, since it is larger than the sum of its proper divisors (80817).

181809 is a wasteful number, since it uses less digits than its factorization.

181809 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20207 (or 20204 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 27.

The square root of 181809 is about 426.3906659391. The cubic root of 181809 is about 56.6506798424.

It can be divided in two parts, 181 and 809, that added together give a triangular number (990 = T₄₄).

The spelling of 181809 in words is "one hundred eighty-one thousand, eight hundred nine".