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 A245903 #14 Jun 03 2018 03:40:49 %S A245903 1,2,10,79,753 %N A245903 Number of permutations of length 2n-1 avoiding 321 that can be realized on increasing binary trees. %C A245903 The number of permutations of length 2n-1 avoiding 321 in the classical sense which can be realized as labels on an increasing binary tree read in the order they appear in a breadth-first search. (Note that breadth-first search reading word is equivalent to reading the tree left to right by levels, starting with the root.) %C A245903 In some cases, more than one tree results in the same breadth-first search reading word, but here we count the permutations, not the trees. %H A245903 Manda Riehl, <a href="/A245903/a245903.png">When n=3, the 10 permutations of length 5 that avoid 321 and can be realized on increasing binary trees.</a> %H A245903 Manda Riehl, <a href="/A245903/a245903.txt">Maple file used to calculate the terms.</a> %e A245903 For n=3, the a(3)= 10 permutations can be read from the sample trees given in the Links section above. %Y A245903 A245903 appears to be the terms of A245900 with odd indices. A245896 is the number of increasing unary-binary trees whose breadth-first reading word avoids 321. %K A245903 nonn,more %O A245903 1,2 %A A245903 _Manda Riehl_, Aug 22 2014