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%I M1622 #33 Feb 23 2021 10:07:10
%S 2,6,18,52,166,524,1722,5664,19072,64408,220676,758864,2634734,
%T 9180872,32208376,113371636,401067522,1423073892,5068961452,
%U 18103192360,64853607912,232872927444,838311889890,3023961593292,10931277735230,39586258360246,143617299291242
%N Number of unrooted triangulations with reflection symmetry of a hexagon with n internal nodes.
%C These are also called [n,3]-triangulations.
%D C. F. Earl and L. J. March, Architectural applications of graph theory, pp. 327-355 of R. J. Wilson and L. W. Beineke, editors, Applications of Graph Theory. Academic Press, NY, 1979.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H Andrew Howroyd, <a href="/A005507/b005507.txt">Table of n, a(n) for n = 0..200</a>
%H C. F. Earl and L. J. March, <a href="/A005500/a005500_1.pdf">Architectural applications of graph theory</a>, pp. 327-355 of R. J. Wilson and L. W. Beineke, editors, Applications of Graph Theory. Academic Press, NY, 1979. (Annotated scanned copy)
%H C. F. Earl & N. J. A. Sloane, <a href="/A005500/a005500.pdf">Correspondence, 1980-1981</a>
%F a(n) = 2 * A005502(n) - A005495(n) (based on _Max Alekseyev_'s formula, cf. A005500 and A005501).
%Y Column k=3 of the array in A169809.
%Y Cf. A005495, A005502.
%K nonn
%O 0,1
%A _N. J. A. Sloane_
%E a(5)-a(10) from _Altug Alkan_ and _Manfred Scheucher_, Mar 08 2018
%E Name clarified and terms a(11) and beyond from _Andrew Howroyd_, Feb 21 2021
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