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 A087945 #8 Aug 21 2021 10:59:20
%S A087945 1,4,14,50,182,670,2482,9226,34358,128078,477698,1782202,6650086,
%T A087945 24816094,92610194,345616490,1289839382,4813708270,17964928162,
%U A087945 67045873306,250218302918,933826814078,3485087904818,13006522708042
%N A087945 Expansion of (1-2x-x^2)/((1-2x)(1-4x+x^2)).
%C A087945 First differences of A087944. Binomial transform of A052948(n+1). a(n)=(2/3)A001834+2^n/3.
%H A087945 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (6,-9,2).
%F A087945 a(0)=1, a(2)=4, a(2)=14, a(n)=6a(n-1)-9a(n-2)+2a(n-3), n>2; a(n)=(2^n+(1-sqrt(3))(2-sqrt(3))^n+(1+sqrt(3))(2+sqrt(3))^n)/3.
%t A087945 CoefficientList[Series[(1-2x-x^2)/((1-2x)(1-4x+x^2)),{x,0,30}],x] (* or *) LinearRecurrence[{6,-9,2},{1,4,14},30] (* _Harvey P. Dale_, Aug 21 2021 *)
%K A087945 easy,nonn
%O A087945 0,2
%A A087945 _Paul Barry_, Sep 16 2003