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 A088421 #4 Mar 30 2012 17:26:10
%S A088421 2,1,5,2,1,5,2,1,4,1,1,3,2,1,1,2,1,2,2,1,5,1,1,5,1,1,4,2,1,1,2,1,3,2,
%T A088421 1,1,2,1,2,1,1,4,1,1,1,2,1,5,2,1,2,2,1,2,1,1,1,1,1,1,2,1,5,1,1,4,2,1,
%U A088421 1,1,1,3,2,1,1,2,1,1,2,1,2,1,1,2,1,1,3,2,1,1,1,1,2,2,1,3,2,1,1,1
%N A088421 Number of primes in arithmetic progression starting with 5 and with d=2n.
%C A088421 Arithmetic progression is stopped when next term is not prime. E.g. for n=3, a=5, that is 5,11,17,23,29 are prime, while next term, 35, is not prime.
%t A088421 bb={}; Do[s=1; Do[If[PrimeQ[5+k*d], s=s+1, bb={bb, s}; Break[]], {k, 10}], {d, 2, 200, 2}]; Flatten[bb]
%Y A088421 Cf. A088420, A088422, A088423, A088424, A088425, A088426, A088427, A088428, A088429.
%K A088421 easy,nonn
%O A088421 1,1
%A A088421 _Zak Seidov_, Sep 29 2003