999809 has 2 divisors, whose sum is σ = 999810. Its totient is φ = 999808.

The previous prime is 999773. The next prime is 999853. The reversal of 999809 is 908999.

It is an a-pointer prime, because the next prime (999853) can be obtained adding 999809 to its sum of digits (44).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 970225 + 29584 = 985^2 + 172^2 .

It is a cyclic number.

It is not a de Polignac number, because 999809 - 2⁸ = 999553 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 999809.

It is not a weakly prime, because it can be changed into another prime (990809) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499904 + 499905.

It is an arithmetic number, because the mean of its divisors is an integer number (499905).

2⁹⁹⁹⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

999809 is a deficient number, since it is larger than the sum of its proper divisors (1).

999809 is an equidigital number, since it uses as much as digits as its factorization.

999809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 52488, while the sum is 44.

The square root of 999809 is about 999.9044954394. The cubic root of 999809 is about 99.9936329279.

The spelling of 999809 in words is "nine hundred ninety-nine thousand, eight hundred nine".