201809 has 2 divisors, whose sum is σ = 201810. Its totient is φ = 201808.

The previous prime is 201797. The next prime is 201821. The reversal of 201809 is 908102.

It is a balanced prime because it is at equal distance from previous prime (201797) and next prime (201821).

It can be written as a sum of positive squares in only one way, i.e., 172225 + 29584 = 415^2 + 172^2 .

It is a cyclic number.

It is not a de Polignac number, because 201809 - 2¹² = 197713 is a prime.

It is a Chen prime.

It is equal to p₁₈₁₂₈ and since 201809 and 18128 have the same sum of digits, it is a Honaker prime.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 201809.

It is not a weakly prime, because it can be changed into another prime (201829) 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 as a sum of consecutive naturals, namely, 100904 + 100905.

It is an arithmetic number, because the mean of its divisors is an integer number (100905).

2²⁰¹⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

201809 is a deficient number, since it is larger than the sum of its proper divisors (1).

201809 is an equidigital number, since it uses as much as digits as its factorization.

201809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 144, while the sum is 20.

The square root of 201809 is about 449.2315661215. The cubic root of 201809 is about 58.6561440896.

The spelling of 201809 in words is "two hundred one thousand, eight hundred nine".