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 A245898 #21 Jun 03 2018 03:39:31 %S A245898 1,1,2,4,10,26,74,217 %N A245898 Number of permutations avoiding 231 that can be realized on increasing unary-binary trees with n nodes. %C A245898 The number of permutations avoiding 231 in the classical sense which can be realized as labels on an increasing unary-binary tree with n nodes 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 A245898 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. %e A245898 For example, when n=4, the permutations 1234, 1243, 1324, and 1423 all avoid 231 in the classical sense and occur as breadth-first search reading words on an increasing unary-binary tree with 4 nodes: %e A245898 1 1 1 1 %e A245898 / \ / \ / \ / \ %e A245898 2 3 2 4 3 2 4 2 %e A245898 | | | | %e A245898 4 3 4 3 %Y A245898 A245901 is the terms of A245898 with odd indices. A245888 is the number of increasing unary-binary trees whose breadth-first reading word avoids 231. %K A245898 nonn,more %O A245898 1,3 %A A245898 _Manda Riehl_, Aug 05 2014