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 A245888 #23 Mar 18 2018 17:38:33 %S A245888 1,1,3,9,36,155,752,3894 %N A245888 Number of labeled increasing unary-binary trees on n nodes whose breadth-first reading word avoids 231. %C A245888 The number of labeled increasing unary-binary trees with an associated permutation avoiding 231 in the classical sense. The tree's permutation is found by recording the labels in the order in which they appear in a breadth-first search. (Note that a breadth-first search reading word is equivalent to reading the tree labels left to right by levels, starting with the root.) %C A245888 In some cases, the same breadth-first search reading permutation can be found on differently shaped trees. This sequence gives the number of trees, not the number of permutations. %H A245888 Manda Riehl, <a href="/A245888/a245888.png">The 9 trees when n = 4.</a> %e A245888 The a(4) = 9 such trees are: %e A245888 : %e A245888 : 1 1 1 1 %e A245888 : /\ /\ /\ /\ %e A245888 : 2 3 2 3 3 2 3 2 %e A245888 : | | | | %e A245888 : 4 4 4 4 %e A245888 : %e A245888 : %e A245888 : 1 1 1 1 1 %e A245888 : /\ /\ | | | %e A245888 : 2 4 4 2 2 2 2 %e A245888 : | | /\ /\ | %e A245888 : 3 3 3 4 4 3 3 %e A245888 : | %e A245888 : 4 %e A245888 : %Y A245888 A245894 gives the number of such binary trees instead of unary-binary trees. %Y A245888 A245898 gives the number of permutations which avoid 231 that are breadth-first reading words on labeled increasing unary-binary trees instead of the number of trees. %K A245888 nonn,more %O A245888 1,3 %A A245888 _Manda Riehl_, Aug 18 2014