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 A355671 #21 Aug 02 2022 23:51:25
%S A355671 0,0,1,0,12,60,570,8190,134456,2408616,49307670,1159112130,
%T A355671 30619757652,891045909468,28244653953698,969331283419590,
%U A355671 35858099428919280,1423688804991442896,60402176709135347502,2726896792761748601226,130498364319404393167820
%N A355671 Number of labeled trees on [n] that are bicentered.
%C A355671 This is the labeled version of A000677 where pertinent definitions can be found.
%H A355671 J. Riordan, <a href="/A007401/a007401_8.pdf">The enumeration of trees by height and diameter</a>, IBM Journal 4 (1960), 473-478. (Annotated scanned copy)
%H A355671 <a href="/index/Tra#trees">Index entries for sequences related to trees</a>
%F A355671 a(n) = Sum_{odd d} A034854(n,d).
%F A355671 a(n) = A000272(n) - A356292(n).
%t A355671 nn = 20; T = NestList[z Exp[#] &, z, nn]; G[k_, z_] := T[[k + 1]];
%t A355671 H[k_, z_] := T[[k + 1]] - T[[k]];H[0, z_] := z; ReplacePart[ Sum[Range[0, nn]! CoefficientList[Series[H[m, z]^2/2, {z, 0, nn}], z], {m, 1, nn/2 - 1}], 3 -> 1]
%Y A355671 Cf. A034854, A000677, A356292, A000272.
%K A355671 nonn
%O A355671 0,5
%A A355671 _Geoffrey Critzer_, Aug 02 2022