686805809 has 2 divisors, whose sum is σ = 686805810. Its totient is φ = 686805808.

The previous prime is 686805793. The next prime is 686805817. The reversal of 686805809 is 908508686.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 670965409 + 15840400 = 25903^2 + 3980^2 .

It is a cyclic number.

It is not a de Polignac number, because 686805809 - 2⁴ = 686805793 is a prime.

It is a super-2 number, since 2×686805809² = 943404438552288962, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (686805709) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 343402904 + 343402905.

It is an arithmetic number, because the mean of its divisors is an integer number (343402905).

Almost surely, 2^686805809 is an apocalyptic number.

It is an amenable number.

686805809 is a deficient number, since it is larger than the sum of its proper divisors (1).

686805809 is an equidigital number, since it uses as much as digits as its factorization.

686805809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 829440, while the sum is 50.

The square root of 686805809 is about 26206.9801579655. The cubic root of 686805809 is about 882.2899248780.

The spelling of 686805809 in words is "six hundred eighty-six million, eight hundred five thousand, eight hundred nine".