209840809 has 4 divisors (see below), whose sum is σ = 222184404. Its totient is φ = 197497216.

The previous prime is 209840783. The next prime is 209840819. The reversal of 209840809 is 908048902.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 78234025 + 131606784 = 8845^2 + 11472^2 .

It is a cyclic number.

It is not a de Polignac number, because 209840809 - 2¹⁵ = 209808041 is a prime.

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (209840819) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6171772 + ... + 6171805.

It is an arithmetic number, because the mean of its divisors is an integer number (55546101).

Almost surely, 2^209840809 is an apocalyptic number.

It is an amenable number.

209840809 is a deficient number, since it is larger than the sum of its proper divisors (12343595).

209840809 is a wasteful number, since it uses less digits than its factorization.

209840809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12343594.

The product of its (nonzero) digits is 41472, while the sum is 40.

The square root of 209840809 is about 14485.8830935501. The cubic root of 209840809 is about 594.2419638359.

The spelling of 209840809 in words is "two hundred nine million, eight hundred forty thousand, eight hundred nine".