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%I M1257 #21 Feb 23 2021 18:03:59
%S 1,2,4,12,33,102,312,1010,3256,10836,36094,122544,417150,1437712,
%T 4970904,17333772,60638124,213435264,753520804,2672606464,9505230397,
%U 33928264990,121400935184,435660446342,1566809204928,5648450745204,20402191885146,73842311224632
%N Number of symmetric trivalent maps with n nodes.
%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="/A005028/b005028.txt">Table of n, a(n) for n = 3..500</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)
%Y Antidiagonal sums of the array in A169809.
%Y Cf. A005027.
%K nonn
%O 3,2
%A _N. J. A. Sloane_
%E Terms a(11) and beyond from _Andrew Howroyd_, Feb 22 2021
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