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A077361
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Smallest n-digit prime whose external digits as well as internal digits form a prime, or 0 if no such number exists.
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2
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0, 0, 127, 1021, 10037, 100057, 1000033, 10000079, 100000037, 1000000021, 10000000033, 100000000057, 1000000000039, 10000000000037, 100000000000031, 1000000000000037, 10000000000000079, 100000000000000021
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OFFSET
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0,3
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COMMENTS
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Conjecture: no entry is zero for n>2.
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LINKS
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MATHEMATICA
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eifpQ[n_]:=Module[{idn=IntegerDigits[n]}, PrimeQ[FromDigits[{First[ idn], Last[ idn]}]]&&PrimeQ[FromDigits[Rest[Most[idn]]]]]; ndp[pwr_]: = Module[ {p=NextPrime[10^pwr]}, While[!eifpQ[p], p=NextPrime[p]]; p]; Join[ {0, 0}, Table[ndp[i], {i, 2, 20}]] (* Harvey P. Dale, Jan 03 2015 *)
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CROSSREFS
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KEYWORD
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base,hard,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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