%I
%S 4,8,20,60,204,748,2860,11180,44204,175788,701100,2800300,11193004,
%T 44755628,178989740,715893420,2863442604,11453508268,45813508780,
%U 183252986540,733009849004,2932035201708,11728132418220,46912512895660
%N Number of corners in a 4sided fractal.
%H Harry J. Smith, <a href="/A060919/b060919.txt">Table of n, a(n) for n=1,...,200</a>
%H H. Bottomley, <a href="/A060919/a060919.gif">Illustration of initial terms</a>
%H <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (7,14,8).
%F a(n) =4^n/6+2^n+4/3 =(2^n+2)*(2^n+4)/6 =4*A007581(n1) =4(a(n1)1)2^n =A028400(n1)A002450(n1)
%F a(n) = 7*a(n1)14*a(n2)+8*a(n3). G.f.: 4*x*(5*x^25*x+1) / ((x1)*(2*x1)*(4*x1)). [_Colin Barker_, Nov 28 2012]
%o (PARI) { for (n=1, 200, write("b060919.txt", n, " ", (2^n + 2)*(2^n + 4)/6); ) } \\ _Harry J. Smith_, Jul 14 2009
%K nonn,easy
%O 1,1
%A _Henry Bottomley_, Apr 10 2001
