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 A139067 #8 Jan 30 2013 10:38:46
%S A139067 2,3,23,223,233,2333,23333,2222333,22222223,223333333,22222222223,
%T A139067 22222223333,22222333333,22223333333,23333333333,222223333333,
%U A139067 23333333333333333,2222222222222233333,2222222222333333333
%N A139067 Primes whose decimal expansion consists of a string of 2's followed by a string of 3's.
%t A139067 With[{nn=20},Sort[Select[Flatten[Table[FromDigits[Join[Table[2,{i}],Table[3,{j}]]],{i,0,nn},{j,0,nn}]],PrimeQ]]] (* _Harvey P. Dale_, Jan 30 2013 *)
%Y A139067 Cf. A020458, A141470, A141471, A141472.
%K A139067 nonn,base
%O A139067 1,1
%A A139067 _Paul Curtz_, Jun 05 2008
%E A139067 Entry revised by _Ray Chandler_ and _N. J. A. Sloane_, Aug 14 2008