scramble prime challenge

[John Keith]

(02-14-2020 10:30 PM)Don Shepherd Wrote:  

(02-14-2020 10:09 PM)John Keith Wrote:  

Code:


Spoilers...










\<< I\->NL DUP { 1. 3. 7. 9. } DIFF
  IF SIZE
  THEN DROP 0.
  ELSE DUP SIZE
    \<< NL\->I ISPRIME?
    \>> DOPERM 0. POS NOT
  END
\>>

thanks John.

What exactly does this program do, I'm not familiar with RPL.
Don

The first 3 lines check for any digits other than 1, 3, 7, or 9 and return 0 (false) if any are present. The next 3 lines create all permutations of the digits of the given number and test if they are prime. If all are prime the program returns 1 (true) else 0 (false).

The documentation for the ListExt Library (see here) explains the commands used better than I can.

As Dave Britten said above, this would get very slow for numbers with more than 6 or 7 digits. Since Albert Chan has shown that there are no scramble primes with more than 3 and less than 19 digits, it's really not that practical anyway.