%I #8 Aug 25 2023 18:50:05
%S 1,1,1,1,4,13,31,61,115,232,505,1117,2413,5089,10660,22477,47779,
%T 101833,216619,459568,974017,2065465,4383769,9307633,19759108,
%U 41934589,88985383,188834389,400758931,850562776,1805202073,3831179989
%N Expansion of (1-x)^2/((1-x)^3-3x^4).
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1,3).
%F G.f. : (1-2x+x^2)/(1-3x+3x^2-x^3-3x^4); a(n)=3a(n-1)-3a(n-2)+a(n-3)+3a(n-4); a(n)=sum{k=0..floor(n/3), binomial(n-k, 3k)3^k}.
%t CoefficientList[Series[(1-x)^2/((1-x)^3-3x^4),{x,0,40}],x] (* or *) LinearRecurrence[{3,-3,1,3},{1,1,1,1},40] (* _Harvey P. Dale_, Aug 25 2023 *)
%K easy,nonn
%O 0,5
%A _Paul Barry_, Jul 25 2004