# Problem 133: Repunit nonfactors
A number consisting entirely of ones is called a repunit. We shall
define R(k) to be a repunit of length k; for example, R(6) = 111111. Let
us consider repunits of the form R(10n). Although R(10), R(100), or
R(1000) are not divisible by 17, R(10000) is divisible by 17. Yet there
is no value of n for which R(10n) will divide by 19. In fact, it is
remarkable that 11, 17, 41, and 73 are the only four primes below
one-hundred that can be a factor of R(10n). Find the sum of all the
primes below one-hundred thousand that will never be a factor of R(10n).