210809 has 2 divisors, whose sum is σ = 210810. Its totient is φ = 210808.

The previous prime is 210803. The next prime is 210811. The reversal of 210809 is 908012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 162409 + 48400 = 403^2 + 220^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-210809 is a prime.

Together with 210811, it forms a pair of twin primes.

It is a Chen prime.

It is a plaindrome in base 16.

It is not a weakly prime, because it can be changed into another prime (210803) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 105404 + 105405.

It is an arithmetic number, because the mean of its divisors is an integer number (105405).

2²¹⁰⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

210809 is a deficient number, since it is larger than the sum of its proper divisors (1).

210809 is an equidigital number, since it uses as much as digits as its factorization.

210809 is an evil number, because the sum of its binary digits is even.

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

The square root of 210809 is about 459.1394123793. The cubic root of 210809 is about 59.5154492284.

The spelling of 210809 in words is "two hundred ten thousand, eight hundred nine".