cp's OEIS Frontend

A046649 a(n) is the number of nonseparable planar maps with 2*n+1 edges and a fixed outer face of 4 edges which are invariant under a rotation of a 1/2 turn. (Column 2 of A091665.)

%I A046649 #22 Mar 30 2021 12:02:34
%S A046649 2,8,34,160,806,4256,23256,130416,746350,4341480,25594530,152585472,
%T A046649 918324904,5572034240,34048494608,209347674768,1294227005694,
%U A046649 8040125464280,50165404177350,314229490307040,1975283452131990,12456968750889600,78790615438385760,499700263517332800
%N A046649 a(n) is the number of nonseparable planar maps with 2*n+1 edges and a fixed outer face of 4 edges which are invariant under a rotation of a 1/2 turn. (Column 2 of A091665.)
%H A046649 Andrew Howroyd, <a href="/A046649/b046649.txt">Table of n, a(n) for n = 2..200</a>
%H A046649 W. G. Brown, <a href="http://dx.doi.org/10.4153/CJM-1963-056-7">Enumeration of non-separable planar maps</a>, Canad. J. Math., 15 (1963), 526-545.
%F A046649 a(n) = 4*(7*n-11)*(3*n-5)!/((n-2)!*(2*n-1)!). - _Emeric Deutsch_, Mar 03 2004
%F A046649 G.f.: 2*(g+1)/(1-g)^3 where g*(1-g)^2 = x. - _Mark van Hoeij_, Nov 10 2011
%Y A046649 Column 2 of A091665.
%K A046649 nonn,easy
%O A046649 2,1
%A A046649 _N. J. A. Sloane_
%E A046649 More terms from _Emeric Deutsch_, Mar 03 2004
%E A046649 Terms a(23) and beyond from _Andrew Howroyd_, Mar 29 2021