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Number of labeled trees on [n] that are centered.
2

%I #10 Aug 04 2022 15:55:02

%S 1,1,0,3,4,65,726,8617,127688,2374353,50692330,1198835561,31297606572,

%T 901114484569,28449258421598,976863784939785,36199494609008656,

%U 1438734246518372897,61037354387458904274,2753490065023053584713,131645635680595606832180

%N Number of labeled trees on [n] that are centered.

%C This is the labeled version of A000676 which has the pertinent definitions.

%H 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 <a href="/index/Tra#trees">Index entries for sequences related to trees</a>

%F a(n) = Sum_{d even} A034854(n,d).

%F a(n) = A000272(n) - A355671(n)

%t nn = 20; T = NestList[z Exp[#] &, z, nn]; G[k_, z_] := T[[k + 1]];H[k_, z_] := T[[k + 1]] - T[[k]];H[0, z_] := z; ReplacePart[ Sum[Range[0, nn]!CoefficientList[Series[G[m, z] (Exp[H[m, z]] - 1 - H[m, z]), {z, 0, nn}], z], {m, 0, nn/2 - 2}], {1 -> 1, 2 -> 1}]

%Y Cf. A034854, A000676, A000272, A355671.

%K nonn

%O 0,4

%A _Geoffrey Critzer_, Aug 02 2022