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 A004057 #17 Sep 08 2022 08:44:32
%S A004057 1,7,39,191,875,3843,16423,68887,285219,1170059,4768127,19336863,
%T A004057 78141883,314953555,1266977751,5089412519,20422176467,81882328731,
%U A004057 328110270895,1314184126255,5261965982571,21063553061987
%N A004057 Expansion of (1-x)/( (1+x)*(1-2*x)*(1-3*x)*(1-4*x)).
%H A004057 Vincenzo Librandi, <a href="/A004057/b004057.txt">Table of n, a(n) for n = 0..1000</a>
%H A004057 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (8,-17,-2,24).
%F A004057 a(n) = (1/30)*(20*2^n - 135*3^n + 144*4^n + (-1)^n).
%t A004057 CoefficientList[Series[(1-x)/((1+x)(1-2x)(1-3x)(1-4x)),{x,0,30}],x] (* or *) LinearRecurrence[{8,-17,-2,24},{1,7,39,191},30] (* _Harvey P. Dale_, Oct 22 2019 *)
%o A004057 (Magma) [(1/30)* (20*2^n - 135*3^n + 144*4^n + (-1)^n): n in [0..30]]; // _Vincenzo Librandi_, Oct 08 2011
%Y A004057 First differences of A099110.
%K A004057 nonn,easy
%O A004057 0,2
%A A004057 _N. J. A. Sloane_