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 A128799 #25 Sep 08 2022 08:45:30
%S A128799 0,0,50,750,7500,62500,468750,3281250,21875000,140625000,878906250,
%T A128799 5371093750,32226562500,190429687500,1110839843750,6408691406250,
%U A128799 36621093750000,207519531250000,1167297363281250,6523132324218750
%N A128799 a(n) = n*(n-1)*5^n.
%H A128799 Vincenzo Librandi, <a href="/A128799/b128799.txt">Table of n, a(n) for n = 0..1000</a>
%H A128799 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (15,-75,125).
%F A128799 G.f.: 50*x^2/(1 - 5*x)^3. - _Vincenzo Librandi_, Feb 10 2013
%F A128799 a(n) = 50*A081135(n). - _R. J. Mathar_, Apr 26 2015
%F A128799 E.g.f.: 25*x^2*exp(5*x). - _G. C. Greubel_, May 17 2021
%F A128799 a(n) = 15*a(n-1) - 75*a(n-2) + 125*a(n-3). - _Wesley Ivan Hurt_, May 17 2021
%p A128799 seq(5^n*n*(n-1), n=0..30); # _G. C. Greubel_, May 17 2021
%t A128799 CoefficientList[Series[50x^2/(1-5x)^3, {x, 0, 30}] ,x] (* _Vincenzo Librandi_, Feb 10 2013 *)
%t A128799 Table[n(n-1)5^n,{n,0,30}] (* or *) LinearRecurrence[{15,-75,125},{0,0,50},30] (* _Harvey P. Dale_, Nov 05 2019 *)
%o A128799 (Magma) [(n^2-n)*5^n: n in [0..20]]; // _Vincenzo Librandi_, Feb 10 2013
%o A128799 (Sage) [2*5^n*binomial(n,2) for n in (0..30)] # _G. C. Greubel_, May 17 2021
%Y A128799 Cf. A007758, A036289, A081135.
%K A128799 nonn,easy
%O A128799 0,3
%A A128799 _Mohammad K. Azarian_, Apr 07 2007