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 A339524 #20 Dec 21 2020 15:36:25 %S A339524 0,1,1,2,3,8,18,49,120,313,802,2120,5591,14942,40033,108108,293094, %T A339524 798839,2185341,6002085,16538599,45716952,126727195,352215812, %U A339524 981268481,2739930091,7666333161,21491833976,60358490615,169798048026,478420333601 %N A339524 Number of unordered pairs of rooted trees with a total of n nodes and an even total of leaves. %C A339524 Equivalently, the number of rooted trees on n+1 nodes, where the root has degree 2, and the number of leaves is even. %H A339524 Washington Bomfim, <a href="/A339524/a339524_1.png">Illustration of initial terms</a> %H A339524 <a href="/index/Ro#rooted">Index entries for sequences related to rooted trees</a> %F A339524 a(n) = A027852(n) - A339525(n). %Y A339524 Cf. A027852, A339525. %K A339524 nonn %O A339524 1,4 %A A339524 _Washington Bomfim_, Dec 08 2020