A005506 - OEIS

%I M2676 #37 Feb 23 2021 10:07:00

%S 1,3,7,19,57,176,557,1806,5954,19897,67235,229366,788688,2730810,

%T 9512107,33309444,117190184,414039578,1468349782,5225201321,

%U 18651958885,66769742002,239643164237,862168692562,3108716586702,11232127258416,40660388117380,147453014455094

%N Number of unrooted triangulations with reflection symmetry of a pentagon with n internal nodes.

%C These are also called [n,2]-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="/A005506/b005506.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 * A005501(n) - A002711(n) (based on _Max Alekseyev_'s formula, cf. A005501).

%Y Column k=2 of the array in A169809.

%Y Cf. A002711, A005501.

%K nonn

%O 0,2

%A _N. J. A. Sloane_

%E a(6)-a(11) from _Altug Alkan_ and _Manfred Scheucher_, Mar 08 2018

%E Name clarified and terms a(12) and beyond from _Andrew Howroyd_, Feb 21 2021