leftTruncatablePrimes.frink

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/** 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
}




View or download leftTruncatablePrimes.frink in plain text format


This is a program written in the programming language Frink.
For more information, view the Frink Documentation or see More Sample Frink Programs.

Alan Eliasen was born 18492 days, 22 hours, 43 minutes ago.