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 A120723 #23 Jul 20 2023 11:16:24
%S A120723 1,11,63,247,887,3207,11383,40679,144663,515719,1835831,6540327,
%T A120723 23289943,82955975,295436919,1052244583,3747563927,13347268359,
%U A120723 47536758199,169305160871,602988299991,2147576619847,7648703663351
%N A120723 Expansion of x*(1+3*x)*(1+6*x+16*x^2)/((1-x)*(1+2*x)*(1-3*x-2*x^2)).
%H A120723 G. C. Greubel, <a href="/A120723/b120723.txt">Table of n, a(n) for n = 1..1000</a>
%H A120723 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,7,-4,-4).
%F A120723 G.f.: x*(1+3*x)*(1+6*x+16*x^2)/((1-x)*(1+2*x)*(1-3*x-2*x^2)). - _Colin Barker_, Apr 04 2012
%F A120723 a(n) = 12*[n=0] - 23/3 + (-2)^n/6 - (9/2)*(A007482(n) - 5*A007482(n- 1)). - _G. C. Greubel_, Jul 20 2023
%t A120723 CoefficientList[Series[(1+3x)*(1 +6x +16x^2)/((1-x)*(1+2x)*(1-3x-2x^2)), {x, 0, 50}], x] (* _Bruno Berselli_, Apr 04 2012 *)
%t A120723 LinearRecurrence[{2,7,-4,-4}, {1,11,63,247}, 40] (* _G. C. Greubel_, Jul 20 2023 *)
%o A120723 (Magma) I:=[1,11,63,247]; [n le 4 select I[n] else 2*Self(n-1) + 7*Self(n-2) -4*Self(n-3) -4*Self(n-4): n in [1..40]]; // _G. C. Greubel_, Jul 20 2023
%o A120723 (SageMath)
%o A120723 A007482=BinaryRecurrenceSequence(3,2,1,3)
%o A120723 def A120723(n): return 12*int(n==0) - (1/6)*(46 - (-2)^n + 27*(A007482(n) - 5*A007482(n-1)))
%o A120723 [A120723(n) for n in range(41)] # _G. C. Greubel_, Jul 20 2023
%Y A120723 Cf. A007482.
%K A120723 nonn,easy
%O A120723 1,2
%A A120723 _Roger L. Bagula_, Aug 17 2006
%E A120723 Edited by _N. J. A. Sloane_, Jun 15 2007
%E A120723 Meaningful name from _Joerg Arndt_, Dec 26 2022