This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A102502 #7 Mar 14 2015 16:59:21
%S A102502 10,13,16,17,20,23,28,31,35,37,46,53,56,61,65,68,74,82,94,95,98,1010,
%T A102502 1013,1018,1042,1048,1051,1052,1063,1072,1073,1082,1103,1114,1124,
%U A102502 1129,1139,1142,1171,1192,1193,1195,1208,1214,1240,1241,1244,1249,1258,1271
%N A102502 Values of n for which the concatenation 9nn9 (from sequence A102484) are primes.
%e A102502 The number 910109 is prime and corresponds to n=10.
%e A102502 The number 9101310139 is prime and corresponds to n=1013.
%t A102502 fQ[n_] := Block[{id = IntegerDigits[n]}, PrimeQ[ FromDigits[ Join[{9}, id, id, {9}]]]]; Select[ Range[1288], fQ[ # ] &] (* _Robert G. Wilson v_, Jan 14 2004 *)
%Y A102502 The full sequence of integers of the form 9nn9 is A102484. The primes that correspond to these values of n are sequence A102503.
%K A102502 easy,nonn,base
%O A102502 1,1
%A A102502 Mark Hudson (mrmarkhudson(AT)hotmail.com), Jan 13 2005
%E A102502 More terms from _Robert G. Wilson v_, Jan 14 2005