1809 has 8 divisors (see below), whose sum is σ = 2720. Its totient is φ = 1188.

The previous prime is 1801. The next prime is 1811. The reversal of 1809 is 9081.

It is not a de Polignac number, because 1809 - 2³ = 1801 is a prime.

It is a Duffinian number.

1809 is a lucky number.

It is a nialpdrome in base 3, base 13, base 14 and base 16.

It is a junction number, because it is equal to n+sod(n) for n = 1791 and 1800.

It is not an unprimeable number, because it can be changed into a prime (1801) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7 + ... + 60.

It is an arithmetic number, because the mean of its divisors is an integer number (340).

2¹⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

1809 is a deficient number, since it is larger than the sum of its proper divisors (911).

1809 is an equidigital number, since it uses as much as digits as its factorization.

1809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 76 (or 70 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 18.

The square root of 1809 is about 42.5323406363. The cubic root of 1809 is about 12.1846443013.

Adding to 1809 its product of nonzero digits (72), we get a palindrome (1881).

The spelling of 1809 in words is "one thousand, eight hundred nine".