Find prime n such that reversed n is also prime: Difference between revisions

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 This program uses the words <code>RVSTR</code> and <code>BPRIM?</code>, respectively made to [[Reverse_a_string#RPL|revert a string]] and to [[Primality_by_trial_division#RPL|test primality by trial division]]
  ≪ { } 1 499 '''FOR''' n
-      '''IF''' n R→B '''BPRIM? THEN'''
+      '''IF''' n R→B '<span style="color:blue">BPRIM?</span> THEN'''
-         '''IF''' n →STR '''RVSTR''' STR→ R→B '''BPRIM? THEN''' n + '''END'''
+         '''IF''' n →STR <span style="color:blue">RVSTR</span> STR→ R→B <span style="color:blue">BPRIM?</span> '''THEN''' n + '''END'''
       '''END'''
    '''NEXT'''
+ ≫ '<span style="color:blue">TASK</span>' STO
- ≫ EVAL
+====Straightforward approach====
+Numbers are here reversed without any string conversion.
+{{works with|HP|49}}
+ « { }
+499 '''FOR''' n
+       '''IF''' n ISPRIME? '''THEN'''
+          n 0
+          '''WHILE''' OVER '''REPEAT'''
+             SWAP 10 IDIV2 ROT 10 * +
+          '''END''' NIP
+          '''IF''' ISPRIME? '''THEN''' n + '''END'''
+       '''END'''
+    '''NEXT'''
+ » '<span style="color:blue">TASK</span>' STO
 {{out}}
 <pre>