str = read["file:pi1000000.txt"] str =~ %s/[^\d]//g // Strip out any non-digits // Largest known is 78073 // "there are no others with n <= 79718" // http://mathworld.wolfram.com/Pi-Prime.html // https://oeis.org/A060421 for len = 79715 to length[str] { s = left[str, len] if isPrime[parseInt[s]] { println["\n*$len\t$s"] exit[] } else print["$len "] }