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 A121204 #18 Nov 30 2022 15:10:22
%S A121204 0,0,20,212,1768,13672,102012,745404,5374160,38400464,272709604,
%T A121204 1928498596,13597146552,95668307256,672119557196,4717043931788,
%U A121204 33080342678944,231867574534048,1624598900644788,11379821699044980
%N A121204 -2n+7^n-5^n.
%H A121204 Vincenzo Librandi, <a href="/A121204/b121204.txt">Table of n, a(n) for n = 0..1000</a>
%H A121204 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (14,-60,82,-35).
%F A121204 G.f.: 4*x^2*(5-17*x)/((1-x)^2 (1-5*x)(1-7*x)). - _Vincenzo Librandi_. Feb 26 2013
%F A121204 a(n) = 14*a(n-1)-60*a(n-2)+82*a(n-3)-35*a(n-4). - _Vincenzo Librandi_, Feb 26 2013
%t A121204 CoefficientList[Series[4 x^2 (5 - 17 x)/((1 - x)^2 (1 - 5 x)(1 - 7 x)), {x, 0, 30}], x] (* _Vincenzo Librandi_, Feb 26 2013 *)
%t A121204 LinearRecurrence[{14,-60,82,-35},{0,0,20,212},20] (* _Harvey P. Dale_, Nov 30 2022 *)
%o A121204 (Magma) I:=[0, 0, 20, 212]; [n le 4 select I[n] else 14*Self(n-1)-60*Self(n-2)+82*Self(n-3)-35*Self(n-4): n in [1..20]]; // _Vincenzo Librandi_, Feb 26 2013
%Y A121204 Cf. A074616.
%K A121204 nonn,easy
%O A121204 0,3
%A A121204 _Mohammad K. Azarian_, Aug 19 2006
%E A121204 Edited by _Ray Chandler_, Sep 06 2006