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 A085278 #36 May 29 2021 02:14:29
%S A085278 1,6,17,38,81,166,337,678,1361,2726,5457,10918,21841,43686,87377,
%T A085278 174758,349521,699046,1398097,2796198,5592401,11184806,22369617,
%U A085278 44739238,89478481,178956966,357913937,715827878,1431655761,2863311526
%N A085278 Expansion of (1+2x)^2/((1-x^2)(1-2x)).
%C A085278 Binomial transform is A085277.
%H A085278 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,1,-2).
%F A085278 a(n)=16*2^n/3+(-1)^n/6-9/2.
%F A085278 G.f.: (2*x+1)^2 / ( (x-1)*(2*x-1)*(1+x) ). - _R. J. Mathar_, Nov 20 2014
%t A085278 CoefficientList[Series[(1+2x)^2/((1-x^2)(1-2x)),{x,0,40}],x] (* or *) LinearRecurrence[{2,1,-2},{1,6,17},40] (* _Harvey P. Dale_, Sep 19 2016 *)
%K A085278 easy,nonn
%O A085278 0,2
%A A085278 _Paul Barry_, Jun 25 2003
%E A085278 Missing parenthesis in definition corrected by _Harvey P. Dale_, Sep 19 2016