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%I #11 Oct 11 2022 22:57:45
%S 0,1,2,6,20,69,241,845,2966,10414,36568,128409,450913,1583401,5560186,
%T 19524854,68562444,240760253,845440977,2968805845,10425101678,
%U 36608235998,128551546480,451414815601,1585164405441
%N Number of LEGO towers, one piece per floor, where every floor is perpendicular to the one below it (so we have a kind of 3-dimensional zigzag pattern).
%H D. Zeilberger, <a href="http://arXiv.org/abs/math.CO/9801016">[math/9801016] Automated counting of LEGO towers</a>
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (5,-6,3,-1).
%F G.f.: x*(1 - 3*x + 2*x^2 - x^3)/(1 - 5*x + 6*x^2 - 3*x^3 + x^4).
%t CoefficientList[Series[x*(1 - 3*x + 2*x^2 - x^3)/(1 - 5*x + 6*x^2 - 3*x^3 + x^4), {x, 0, 30}], x] (* _Wesley Ivan Hurt_, Feb 12 2017 *)
%t LinearRecurrence[{5,-6,3,-1},{0,1,2,6,20},30] (* _Harvey P. Dale_, Nov 10 2021 *)
%K nonn,easy
%O 0,3
%A _Ralf Stephan_, May 19 2003
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