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 A183421 #8 Mar 30 2012 18:57:12 %S A183421 1,7,3,79,10,23,5,6559,88,142,13,623,28,47,8,43046719,6640,8098,97, %T A183421 20734,154,223,17,390623,648,898,33,2399,54,98,11 %N A183421 Second of two complementary trees generated by the squares; The other tree is A183420. %C A183421 See A183420. %F A183421 See the formulas at A183169 and A183423. %e A183421 First three levels: %e A183421 .............1 %e A183421 ........7............3 %e A183421 .....79...10......23.....5 %Y A183421 Cf. A183420, A183169, A183423. %K A183421 nonn,tabf %O A183421 1,2 %A A183421 _Clark Kimberling_, Jan 04 2011