%I #17 Sep 08 2022 08:44:49

%S 1,1,2,4,6,11,20,33,59,104,178,314,549,952,1669,2913,5074,8872,15482,

%T 27007,47172,82325,143675,250848,437822,764198,1334041,2328512,

%U 4064457,7094833,12384034,21616716,37732990,65863651

%N Sum{T(n-k,k)}, 0<=k<=[ n/2 ], where T is the array in A026374.

%H Vincenzo Librandi, <a href="/A026385/b026385.txt">Table of n, a(n) for n = 0..1000</a>

%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,1,3,1).

%F G.f.: (1+x+x^2)/(1-x^2-3x^3-x^4). - _Ralf Stephan_, Apr 30 2004

%F a(n) = a(n-2) + 3*a(n-3) + a(n-4) for n>3. - _Vincenzo Librandi_, Jun 19 2014

%t LinearRecurrence[{0,1,3,1},{1,1,2,4},40] (* _Harvey P. Dale_, Jun 18 2014 *)

%t CoefficientList[Series[(1 + x + x^2)/(1 - x^2 - 3 x^3 - x^4), {x, 0, 40}], x] (* _Vincenzo Librandi_, Jun 19 2014 *)

%o (Magma) I:=[1,1,2,4]; [n le 4 select I[n] else Self(n-2)+3*Self(n-3)+Self(n-4): n in [1..40]]; // _Vincenzo Librandi_, Jun 19 2014

%K nonn

%O 0,3

%A _Clark Kimberling_