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 A003227 M2744 #33 Feb 16 2025 08:32:27
%S A003227 1,1,3,8,22,58,160,434,1204,3341,9363,26308,74376,210823,599832,
%T A003227 1710803,4891876,14015505,40231632,115669419,333052242,960219982,
%U A003227 2771707332,8009222307,23166563032,67069289457,194332834601
%N A003227 Endpoints (leaves) in rooted trees with n nodes.
%C A003227 Number of unlabeled rooted trees with n nodes and a distinguished leaf. - _Gus Wiseman_, Jul 31 2018
%D A003227 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A003227 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 A003227 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/TreeLeaf.html">Tree Leaf</a>.
%H A003227 <a href="/index/Ro#rooted">Index entries for sequences related to rooted trees</a>
%H A003227 <a href="/index/Tra#trees">Index entries for sequences related to trees</a>
%F A003227 a(n) = Sum_{k=1..n} k*A055277(n, k).
%e A003227 The a(4) = 8 rooted trees with a distinguished leaf are (((O))), ((Oo)), ((oO)), (O(o)), (o(O)), (Ooo), (oOo), (ooO). - _Gus Wiseman_, Jul 31 2018
%t A003227 urt[n_]:=Join@@Table[Union[Sort/@Tuples[urt/@ptn]],{ptn,IntegerPartitions[n-1]}];
%t A003227 Table[Sum[Length[Flatten[{t/.{}->1}]],{t,urt[n]}],{n,15}] (* _Gus Wiseman_, Jul 31 2018 *)
%Y A003227 Cf. A000081, A003228, A004111, A038046, A055277, A317580.
%K A003227 nonn
%O A003227 1,3
%A A003227 _N. J. A. Sloane_
%E A003227 Corrected and extended with formula by _Christian G. Bower_, May 25 2000