A109627 - OEIS

%I #6 Dec 15 2017 17:36:54

%S 91,9091,9271,9451,900991,907291,914581,917281,920971,931861,939061,

%T 943651,954541,958141,960931,972721,975421,977221,978121,982711,

%U 90027991,90209791,90272791,90372691,90381691,90627391,90745291

%N Numbers n such that concatenation of n and its 10's complement is a palindromic prime.

%C 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

%H Keith Schneider (schneidk(AT)unc.edu), May 20 2007, <a href="/A109627/b109627.txt">Table of n, a(n) for n = 1..108</a>

%e a(3)=9271 because 10^4-9271 = 729 and concatenating produces the palprime 9271729.

%t Mathematica code from Keith Schneider, May 21 2007:

%t Remove[PalList, PrimeList, SeqList]

%t PalList[n_] := PalList[n] = Table[FromDigits[Join[Join[{9},

%t 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}];

%t PrimeList[n_] := PrimeList[n] = Delete[Union[Table[If[ PrimeQ[PalList[n][[ i]]], PalList[n][[i]]], {i, 1, Length[PalList[n]]}]], -1];

%t SeqList[2] = {91};

%t SeqList[n_] := SeqList[n] = Table[FromDigits[IntegerDigits[ PrimeList[n][[i]]][[Range[n]]]], {i, 1, Length[PrimeList[n]]}];

%t TheList = Join[SeqList[2], SeqList[4], SeqList[6], SeqList[8],

%t SeqList[10], SeqList[12], SeqList[14]]; TheList // TableForm

%t Length[TheList]

%K base,nonn

%O 1,1

%A _Jason Earls_, Aug 02 2005

%E More terms from Keith Schneider (schneidk(AT)unc.edu), May 20 2007, May 21 2007