This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A084861 #8 Nov 25 2020 19:09:06
%S A084861 1,1,4,9,21,48,108,240,528,1152,2496,5376,11520,24576,52224,110592,
%T A084861 233472,491520,1032192,2162688,4521984,9437184,19660800,40894464,
%U A084861 84934656,176160768,364904448,754974720,1560281088,3221225472
%N A084861 Expansion of (1-3x+4x^2-3x^3+x^4)/(1-2x)^2.
%C A084861 Partial sums give A084860. Binomial transform of signed version of A008795.
%H A084861 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (4,-4).
%F A084861 a(n) = 3(n+3)2^(n-4), n>2.
%t A084861 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 A084861 easy,nonn
%O A084861 0,3
%A A084861 _Paul Barry_, Jun 12 2003