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 A032668 #11 Sep 03 2017 03:21:06
%S A032668 3,9,21,23,41,47,57,63,69,71,77,87,93,99,101,107,113,119,147,153,167,
%T A032668 171,179,189,197,209,227,231,233,237,261,273,279,281,297,303,309,323,
%U A032668 333,347,351,381,387,393,399,407,413,417,419,431,437,441
%N A032668 Digit '5' concatenated with a(n) is a prime.
%H A032668 Seiichi Manyama, <a href="/A032668/b032668.txt">Table of n, a(n) for n = 1..10000</a>
%t A032668 Select[Range[500],PrimeQ[FromDigits[Join[{5},IntegerDigits[#]]]]&] (* _Harvey P. Dale_, Mar 23 2012 *)
%K A032668 nonn,base
%O A032668 1,1
%A A032668 _Patrick De Geest_, May 15 1998