/** This program finds left-truncatable primes, that is, prime numbers that
    always produce prime numbers when their leftmost digit is chopped off.
    This builds them from a starting set of primes and will find all
    left-truncatable primes.  Zero is not allowed as a digit in this
    formulation, which produces a finite number of solutions.
*/
testPrime[nums] :=
{
   result = new array
   for d = [1,2,3,4,5,6,7,8,9]
   {
      for n = nums
      {
	 c = parseInt["$d$n"]
	 if isPrime[c] and c != 1
	    result.push[c]
      }
   }
   return result
}

results = [1,2,3,5,7]
digits = 1
while (length[results] != 0)
{
   newresults = new array
   newresults = testPrime[results]

   println["$digits\t" + length[newresults] + "\t" + newresults]
   results = newresults
   digits = digits + 1
}