Pandigital prime: Difference between revisions
add RPL
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The largest 0..7 pandigital prime is 76540231 20.30 ms
done...</pre>
=={{header|RPL}}==
Based on Factor's insights, we only need to check 4- and 7-digit pandigitals from biggest to smallest.
Rather than generating permutations, we start from the biggest pandigital number for a given number of digits and go backwards by increment of 18, since:
* the difference between 2 pandigital numbers is a multiple of 9
* the biggest pandigital number for a given number of digits is odd and lower candidate numbers must also be odd
{{works with|HP|49}}
« R→I →STR DUP SIZE → d s
« 0
1 s '''FOR''' j
d j DUP SUB STR→ ALOG + '''NEXT''' <span style="color:grey">@ count digit occurrences into a unique number</span>
10 / 9 * 1 + LOG FP NOT <span style="color:grey">@ check that the result is a repunit</span>
» » '<span style="color:blue">ISPAND?</span>' STO
« 0
'''WHILE''' OVER '''REPEAT'''
10 * OVER + SWAP 1 - SWAP '''END'''
NIP 1 CF
DUP XPON ALOG '''FOR''' n
'''IF''' n ISPRIME? '''THEN'''
'''IF''' n <span style="color:blue">ISPAND?</span> '''THEN''' 1 SF n DUP XPON ALOG 'n' STO
'''END END'''
-18 '''STEP'''
'''IF''' 1 FC? '''THEN''' 0 '''END'''
» '<span style="color:blue">PANPRIME</span>' STO
« 7 <span style="color:blue">PANPRIME</span>
'''IF''' DUP NOT '''THEN''' 4 <span style="color:blue">PANPRIME</span> '''END'''
» 'P041' STO
{{out}}
<pre>
1: 7652413
</pre>
=={{header|Ruby}}==
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