990809 has 2 divisors, whose sum is σ = 990810. Its totient is φ = 990808.

The previous prime is 990799. The next prime is 990841. The reversal of 990809 is 908099.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 990025 + 784 = 995^2 + 28^2 .

It is a cyclic number.

It is not a de Polignac number, because 990809 - 2¹⁶ = 925273 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a plaindrome in base 15.

It is not a weakly prime, because it can be changed into another prime (990889) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495404 + 495405.

It is an arithmetic number, because the mean of its divisors is an integer number (495405).

2⁹⁹⁰⁸⁰⁹ is an apocalyptic number.

It is an amenable number.

990809 is a deficient number, since it is larger than the sum of its proper divisors (1).

990809 is an equidigital number, since it uses as much as digits as its factorization.

990809 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5832, while the sum is 35.

The square root of 990809 is about 995.3938918840. The cubic root of 990809 is about 99.6926899058.

It can be divided in two parts, 9 and 90809, that multiplied together give a triangular number (817281 = T₁₂₇₈).

The spelling of 990809 in words is "nine hundred ninety thousand, eight hundred nine".