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 A233764 #25 Jul 21 2017 00:45:39 %S A233764 0,1,3,5,9,11,15,21,29,31,35,41,51,61,69,83,99,101,105,111,121,131, %T A233764 141,159,183,201,209,223,245,271,287,317,349,351,355,361,371,381,391, %U A233764 409,433,451,461,479,507,545,575,625,679,713,721,735,757,783 %N A233764 Number of toothpicks and D-toothpicks after n-th stage in a D-toothpick "wide" triangle (see Comments lines for definition). %C A233764 The D-toothpicks placed in northwest or northeast direction both are prohibited. Note that due this rule there are substructures with broken symmetry, for instance a(44) = 507, not 509. For another version without broken symmetry see A233780. %C A233764 A233765 (the first differences) gives the number of toothpicks or D-toothpicks added at n-th stage. %C A233764 First differs from A169780 at a(24). %C A233764 First differs from A233970 at a(25). %C A233764 First differs from A233780 at a(44). %H A233764 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 A233764 <a href="/index/To#toothpick">Index entries for sequences related to toothpick sequences</a> %Y A233764 Cf. A139250, A169780, A220500, A220520, A231348, A233765, A233780, A233970. %K A233764 nonn %O A233764 0,3 %A A233764 _Omar E. Pol_, Dec 16 2013