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Search: id:A109627
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| A109627 |
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Numbers n such that concatenation of n and its 10's complement is a palindromic prime. |
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1
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| 91, 9091, 9271, 9451, 900991, 907291, 914581, 917281, 920971, 931861, 939061, 943651, 954541, 958141, 960931, 972721, 975421, 977221, 978121, 982711, 90027991, 90209791, 90272791, 90372691, 90381691, 90627391, 90745291
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The Mathematica code can be modified to verify that the included list is a complete listing of the sequence such that a(n) < 100000000. - Keith Schneider (schneidk(AT)unc.edu), May 20 2007, May 21 2007
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LINKS
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Keith Schneider (schneidk(AT)unc.edu), May 20 2007, Table of n, a(n) for n = 1..108
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EXAMPLE
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a(3)=9271 because 10^4-9271 = 729 and concatenating produces the palprime 9271729.
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MATHEMATICA
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Mathematica code from Keith Schneider, May 21 2007:
Remove[PalList, PrimeList, SeqList]
PalList[n_] := PalList[n] = Table[FromDigits[Join[Join[{9},
PadLeft[IntegerDigits[i], n/2 - 1], Reverse[ PadLeft[IntegerDigits[ 10^(n/2 - 1) - 1 - i], n/2 - 1]], {1}], Reverse[Join[{9}, PadLeft[IntegerDigits[i], n/2 - 1], Reverse[ PadLeft[IntegerDigits[10^(n/2 - 1) - 1 - i], n/2 - 1]]]]]], { i, 0, 10^(n/2 - 1) - 10^(n/2 - 2) - 1}];
PrimeList[n_] := PrimeList[n] = Delete[Union[Table[If[ PrimeQ[PalList[n][[ i]]], PalList[n][[i]]], {i, 1, Length[PalList[n]]}]], -1];
SeqList[2] = {91};
SeqList[n_] := SeqList[n] = Table[FromDigits[IntegerDigits[ PrimeList[n][[i]]][[Range[n]]]], {i, 1, Length[PrimeList[n]]}];
TheList = Join[SeqList[2], SeqList[4], SeqList[6], SeqList[8],
SeqList[10], SeqList[12], SeqList[14]]; TheList // TableForm
Length[TheList]
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CROSSREFS
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Sequence in context: A060078 A006244 A054216 this_sequence A095372 A015261 A131442
Adjacent sequences: A109624 A109625 A109626 this_sequence A109628 A109629 A109630
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KEYWORD
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base,nonn
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AUTHOR
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Jason Earls (zevi_35711(AT)yahoo.com), Aug 02 2005
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EXTENSIONS
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More terms from Keith Schneider (schneidk(AT)unc.edu), May 20 2007, May 21 2007
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