18509 has 4 divisors (see below), whose sum is σ = 18816. Its totient is φ = 18204.

The previous prime is 18503. The next prime is 18517. The reversal of 18509 is 90581.

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, and also an emirpimes, since its reverse is a distinct semiprime: 90581 = 239 ⋅379.

It is a cyclic number.

It is not a de Polignac number, because 18509 - 2⁴ = 18493 is a prime.

It is an alternating number because its digits alternate between odd and even.

It is a Duffinian number.

It is a Curzon number.

It is a nialpdrome in base 12.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18503) 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, 29 + ... + 194.

It is an arithmetic number, because the mean of its divisors is an integer number (4704).

2¹⁸⁵⁰⁹ is an apocalyptic number.

It is an amenable number.

18509 is a deficient number, since it is larger than the sum of its proper divisors (307).

18509 is an equidigital number, since it uses as much as digits as its factorization.

18509 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 306.

The product of its (nonzero) digits is 360, while the sum is 23.

The square root of 18509 is about 136.0477857225. The cubic root of 18509 is about 26.4521505107.

The spelling of 18509 in words is "eighteen thousand, five hundred nine".