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%I
%S 1,8,29,85,232,617,1625,4264,11173,29261,76616,200593,525169,1374920,
%T 3599597,9423877,24672040,64592249,169104713,442721896,1159060981,
%U 3034461053,7944322184,20798505505
%N Crystal ball sequence for hyperbolic tesselation 3^7 (from triangle group (2,3,7)).
%H <a href="/index/Cor#crystal_ball">Index entries for crystal ball sequences</a>
%F Conjecture: a(n) = 4*a(n-1)-4*a(n-2)+a(n-3). G.f.: (1+4*x+x^2)/((1-x)*(1-3*x+x^2)). [Colin Barker, Mar 16 2012]
%Y Cf. A001354.
%K nonn,easy,nice
%O 0,2
%A _N. J. A. Sloane_.
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