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 A209643 #12 Dec 13 2015 17:38:03 %S A209643 0,1,2,3,4,6,7,8,9,14,16,17,19,20,21,22,23,37,42,44,45,51,53,54,56,57, %T A209643 58,60,61,62,63,64,65,107,121,126,128,129,149,154,156,157,163,165,166, %U A209643 168,169,170,177,179,180,182,183,184,186,187,188,189,191,192,193,194,195,196,197,329,371,385,390,392,393,461,475,480,482 %N A209643 A014486-indices for rooted plane trees where non-leaf branching can occur only at the leftmost branch of any level, but nowhere else. %C A209643 5 is not member of this sequence, as it encodes in A014486 a general tree: %C A209643 ..| %C A209643 \/ %C A209643 which has a nonempty branch which is not the leftmost child of its parent vertex. %H A209643 Antti Karttunen, <a href="/A209643/b209643.txt">Table of n, a(n) for n = 0..32767</a> %H A209643 A. Karttunen, <a href="/A014486/a014486.pdf">Corresponding trees illustrated on 1, 2, 3, 4, 6, 7, 8, 9, 14, 16, 17th, etc. row in this illustration.</a> %F A209643 a(n) = A080300(A209641(n)). %Y A209643 Cf. A209644, A071163. %K A209643 nonn %O A209643 0,3 %A A209643 _Antti Karttunen_, Mar 24 2012