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 A109548 #8 Aug 03 2014 14:26:15
%S A109548 11,31,41,331,2221,3331,4441,33331,333331,3333331,33333331,
%T A109548 44444444441,555555555551,5555555555551,222222222222222221,
%U A109548 333333333333333331,1111111111111111111,11111111111111111111111
%N A109548 Primes of the form aaaa...aa1 where a is 1, 2, 3, 4 or 5.
%H A109548 Vincenzo Librandi, <a href="/A109548/b109548.txt">Table of n, a(n) for n = 1..38</a>
%F A109548 d=1, 2, 3, 4, 5 a(n) = if prime then Sum[d*10^i, {i, 1, m}] + 1
%t A109548 d[n_] = Mod[n, 6] a = Flatten[Table[Sum[d[k]*10^i, {i, 1, m}] + 1, {m, 1, 50}, {k, 1, 5}]] b = Flatten[Table[If[PrimeQ[a[[i]]] == True, a[[i]], {}], {i, 1, Length[a]}]]
%t A109548 Select[FromDigits/@Flatten[Table[PadLeft[{1},i,#]&/@{1,2,3,4,5},{i,2,80}],1],PrimeQ[#]&] (* _Vincenzo Librandi_, Dec 12 2011 *)
%Y A109548 Cf. A051200, A004022, A093176, A093177, A089346, A093174, A092571, A089345, A089347.
%K A109548 nonn
%O A109548 1,1
%A A109548 _Roger L. Bagula_, Jun 26 2005