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
}




Download or view 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 19349 days, 5 hours, 13 minutes ago.