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 A003228 M0351 #26 Feb 16 2025 08:32:27
%S A003228 1,2,2,5,9,21,43,101,226,556,1333,3365,8500,22007,57258,151264,401761,
%T A003228 1077063,2902599,7871250,21440642,58672589,161155637,444240627,
%U A003228 1228400744,3406668865,9472308269,26402207803,73755064178
%N A003228 Endpoints in trees with n nodes.
%D A003228 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A003228 R. W. Robinson and A. J. Schwenk, <a href="https://doi.org/10.1016/0012-365X(75)90076-X">The distribution of trees in a large random tree</a>, Discr. Math., 12 (1975), 359-372.
%H A003228 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TreeLeaf.html">Tree Leaf</a>.
%H A003228 <a href="/index/Tra#trees">Index entries for sequences related to trees</a>
%F A003228 a(n) = Sum_{k=1..n} k*c(n, k), where c(n, k) = A055290(n, k) has g.f. (1-x+x*y)*B(x, y)+(1/2)*(B(x^2, y^2)-B(x, y)^2) and B(x, y) is g.f. for A055372.
%Y A003228 Cf. A000055, A003227, A055290, A055372.
%K A003228 nonn
%O A003228 1,2
%A A003228 _N. J. A. Sloane_
%E A003228 Corrected and extended with formula by _Christian G. Bower_, May 25 2000