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 A222173 #15 Mar 24 2013 14:01:30 %S A222173 0,1,1,1,2,3,2,1,2,4,4,3,5,7,4,1,2,4,6,8 %N A222173 Number of pentagons added at n-th stage to the structure of A222172. %C A222173 Essentially the first differences of A222172. %C A222173 Also number of P-toothpicks added at n-th stage to the P-toothpick structure of A222172. %C A222173 First differs from A152978 at a(9). %H A222173 N. J. A. Sloane, <a href="/wiki/Catalog_of_Toothpick_and_CA_Sequences_in_OEIS">Catalog of Toothpick and Cellular Automata Sequences in the OEIS</a> %H A222173 <a href="/index/To#toothpick">Index entries for sequences related to toothpick sequences</a> %F A222173 a(n) = A222181(n+2)/10 = A222177(n+1)/2, n >= 1. %e A222173 Apparently this is an irregular triangle: %e A222173 0; %e A222173 1, 1; %e A222173 1, 2, 3, 2; %e A222173 1, 2, 4, 4, 3, 5, 7, 4; %e A222173 1, 2, 4, 6, 8,... %Y A222173 Cf. A139251, A152978, A222172, A222177, A222180, A222181. %K A222173 nonn,tabf,more %O A222173 0,5 %A A222173 _Omar E. Pol_, Mar 21 2013