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Expansion of (1-3x+4x^2-3x^3+x^4)/(1-2x)^2.
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%I #8 Nov 25 2020 19:09:06

%S 1,1,4,9,21,48,108,240,528,1152,2496,5376,11520,24576,52224,110592,

%T 233472,491520,1032192,2162688,4521984,9437184,19660800,40894464,

%U 84934656,176160768,364904448,754974720,1560281088,3221225472

%N Expansion of (1-3x+4x^2-3x^3+x^4)/(1-2x)^2.

%C Partial sums give A084860. Binomial transform of signed version of A008795.

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (4,-4).

%F a(n) = 3(n+3)2^(n-4), n>2.

%t CoefficientList[Series[(1-3x+4x^2-3x^3+x^4)/(1-2x)^2,{x,0,40}],x] (* or *) LinearRecurrence[{4,-4},{1,1,4,9,21},40] (* _Harvey P. Dale_, Nov 25 2020 *)

%K easy,nonn

%O 0,3

%A _Paul Barry_, Jun 12 2003