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Expansion of (1 + x^2)*(1 + 2*x)/(1 - x^2).
1

%I #11 Feb 06 2024 11:57:44

%S 1,2,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,

%T 2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,

%U 2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4,2,4

%N Expansion of (1 + x^2)*(1 + 2*x)/(1 - x^2).

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,1).

%F a(0)=1, a(n)=(2-0^((n-1)/2))(1-(-1)^n)+(2-0^(n/2))(1+(-1)^n)/2, n>1.

%t CoefficientList[Series[(1+x^2)(1+2x)/(1-x^2),{x,0,95}],x] (* _James C. McMahon_, Feb 02 2024 *)

%Y Row sums of A106468.

%K easy,nonn

%O 0,2

%A _Paul Barry_, May 03 2005