A090401 - OEIS

%I #8 Jun 13 2015 00:51:16

%S 1,3,9,27,78,225,648,1863,5355,15390,44226,127089,365202,1049436,

%T 3015630,8665623,24901263,71555481,205619553,590861790,1697881581,

%U 4878978300,14020076241,40287643353,115769285316,332670921048

%N Expansion of 1/(1-3x+3x^4).

%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (3,0,0,-3).

%F a(n)=3a(n-1)-3a(n-4); a(n)=sum{k=0..floor(n/2), comb(n-3k, k)3^(n-3k) }.

%t CoefficientList[Series[1/(1-3x+3x^4),{x,0,30}],x] (* or *) LinearRecurrence[ {3,0,0,-3},{1,3,9,27},30] (* _Harvey P. Dale_, Apr 19 2015 *)

%K easy,nonn

%O 0,2

%A _Paul Barry_, Nov 28 2003