+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.
+Given 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.
+You 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.
+However, there are rare composite values for which this is also true; the first
+five examples being 91, 259, 451, 481, and 703.
+Find the sum of the first twenty-five composite values of n for which GCD(n,
+10) = 1 and n − 1 is divisible by A(n).
+ $mod = (($mod * 10 + 1) % $n);
+open my $primes_fh, "primes 3|";
+my $last_prime = int(scalar(<$primes_fh>));
+ $last_prime = int(scalar(<$primes_fh>));
+ if (($n - 1) % $A == 0)
+ print "Found $n ; Sum = $sum ; Count = $count\n";