%I #16 Feb 02 2024 08:56:09

%S 1,3,8,18,40,84,182,378,814,1686,3626,7506,16138,33402,71810,148626,

%T 319522,661314,1421714,2942514,6325906,13092690,28147058,58255794,

%U 125240050,259208562,557254322,1153345842,2479497394

%N a(n) = Sum_{i=0..n, j=0..n} A026648(i,j).

%H <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (1,4,-4,2,-2).

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

%t LinearRecurrence[{1, 4, -4, 2, -2}, {1, 3, 8, 18, 40}, 50] (* _Paolo Xausa_, Feb 02 2024 *)

%Y Cf. A026648.

%K nonn

%O 0,2

%A _Clark Kimberling_