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 A164039 #15 Sep 09 2017 03:22:29
%S A164039 1,2,4,9,23,64,186,551,1645,4926,14768,44293,132867,398588,1195750,
%T A164039 3587235,10761689,32285050,96855132,290565377,871696111,2615088312,
%U A164039 7845264914,23535794719,70607384133,211822152374,635466457096
%N A164039 a(n+1) = 3*a(n) - n.
%H A164039 G. C. Greubel, <a href="/A164039/b164039.txt">Table of n, a(n) for n = 0..1000</a>
%H A164039 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (5,-7,3).
%F A164039 a(0) = 1; a(n+1) = 3*a(n) - n.
%F A164039 a(n) = (3^n + 2*n + 3)/4.
%F A164039 From _R. J. Mathar_, Aug 09 2009: (Start)
%F A164039 a(n) = 5*a(n-1)-7*a(n-2)+3*a(n-3).
%F A164039 G.f.: (1-3*x+x^2)/((1-3*x)*(1-x)^2). (End)
%F A164039 E.g.f.: (1/4)*((2*x + 3)*exp(x) + exp(3*x)). - _G. C. Greubel_, Sep 08 2017
%t A164039 Transpose[NestList[Flatten[{Rest[#],ListCorrelate[#,{3,-7,5}]}]&, {1,2,4},30]][[1]] (* _Harvey P. Dale_, Mar 24 2011 *)
%t A164039 Table[(3^n + 2*n + 3)/4, {n,0,50}] (* _G. C. Greubel_, Sep 08 2017 *)
%o A164039 (PARI) x='x+O('x^50); Vec((1-3*x+x^2)/((1-3*x)*(1-x)^2)) \\ _G. C. Greubel_, Sep 08 2017
%K A164039 nonn,easy
%O A164039 0,2
%A A164039 _Rolf Pleisch_, Aug 08 2009