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 A128786 #17 Sep 08 2022 08:45:30
%S A128786 0,7,196,3087,38416,420175,4235364,40353607,368947264,3268642167,
%T A128786 28247524900,239256535903,1993145356944,16374242758783,
%U A128786 132931722278404,1068201339737175,8507630225817856,67230218542302823,527606005722985476
%N A128786 n^2*7^n.
%H A128786 Vincenzo Librandi, <a href="/A128786/b128786.txt">Table of n, a(n) for n = 0..1000</a>
%H A128786 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (21,-147,343).
%F A128786 G.f.: 7*x*(1 + 7*x)/((1 - 7*x)^3). - _Vincenzo Librandi_, Feb 06 2013
%F A128786 a(n) = 21*a(n-1) - 147*a(n-2) + 343*a(n-3). - _Vincenzo Librandi_, Feb 06 2013
%t A128786 LinearRecurrence[{21, -147, 343}, {0, 7, 196}, 40] (* _Vincenzo Librandi_, Feb 06 2013 *)
%o A128786 (Magma) [n^2*7^n: n in [0..20]]; // _Vincenzo Librandi_, Feb 06 2013
%Y A128786 Cf. A036289; A007758.
%K A128786 nonn,easy
%O A128786 0,2
%A A128786 _Mohammad K. Azarian_, Apr 07 2007