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 A019928 #15 Jan 23 2025 10:24:49
%S A019928 1,20,269,3040,31161,300300,2775109,24887960,218303921,1882786180,
%T A019928 16026538749,135010883280,1127921219881,9359429537660,77233958267189,
%U A019928 634411837477000,5191228487083041,42342127346986740
%N A019928 Expansion of 1/((1-5x)(1-7x)(1-8x)).
%H A019928 Vincenzo Librandi, <a href="/A019928/b019928.txt">Table of n, a(n) for n = 0..200</a>
%H A019928 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (20,-131,280).
%F A019928 a(n) = 25*5^n/6 -49*7^n/2 +64*8^n/3. - _R. J. Mathar_, Jun 29 2013
%F A019928 a(0)=1, a(1)=20, a(2)=269; for n>2, a(n) = 20*a(n-1) -131*a(n-2) +280*a(n-3). - _Vincenzo Librandi_, Jul 03 2013
%F A019928 a(n) = 15*a(n-1) -56*a(n-2) +5^n. - _Vincenzo Librandi_, Jul 03 2013
%t A019928 CoefficientList[Series[1 / ((1 - 5 x) (1 - 7 x) (1 - 8 x)), {x, 0, 20}], x] (* _Vincenzo Librandi_, Jul 03 2013 *)
%o A019928 (Magma) m:=20; R<x>:=PowerSeriesRing(Integers(), m); Coefficients(R!(1/((1-5*x)*(1-7*x)*(1-8*x)))); // _Vincenzo Librandi_, Jul 03 2013
%o A019928 (Magma) I:=[1, 20, 269]; [n le 3 select I[n] else 20*Self(n-1)-131*Self(n-2)+280*Self(n-3): n in [1..20]]; // _Vincenzo Librandi_, Jul 03 2013
%K A019928 nonn,easy
%O A019928 0,2
%A A019928 _N. J. A. Sloane_