yaworsw/euler-manager

---
:id: 130
:name: Composites with prime repunit property
:url: https://projecteuler.net/problem=130
:content: "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.\n\nGiven that
  _n_ is a positive integer and GCD(_n_, 10) = 1, it can be shown that there always
  exists a value, _k_, for which R(_k_) is divisible by _n_, and let A(_n_) be the
  least such value of _k_; for example, A(7) = 6 and A(41) = 5.\n\nYou are given that
  for all primes, _p_ \\> 5, that _p_ − 1 is divisible by A(_p_). For example, when
  _p_ = 41, A(41) = 5, and 40 is divisible by 5.\n\nHowever, there are rare composite
  values for which this is also true; the first five examples being 91, 259, 451,
  481, and 703.\n\nFind the sum of the first twenty-five composite values of _n_ for
  which  \nGCD(_n_, 10) = 1 and _n_ − 1 is divisible by A(_n_).\n\n"