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 A037681 #10 May 10 2023 16:13:07
%S A037681 1,4,19,78,313,1252,5011,20046,80185,320740,1282963,5131854,20527417,
%T A037681 82109668,328438675,1313754702,5255018809,21020075236,84080300947,
%U A037681 336321203790,1345284815161,5381139260644,21524557042579,86098228170318
%N A037681 Base-4 digits are, in order, the first n terms of the periodic sequence with initial period 1,0,3,2.
%H A037681 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (4,0,0,1,-4).
%F A037681 G.f.: x*(1+3*x^2+2*x^3) / ( (x-1)*(4*x-1)*(1+x)*(x^2+1) ). - _R. J. Mathar_, May 04 2015
%t A037681 Table[FromDigits[PadRight[{},n,{1,0,3,2}],4],{n,30}] (* or *) LinearRecurrence[{4,0,0,1,-4},{1,4,19,78,313},30] (* _Harvey P. Dale_, May 10 2023 *)
%K A037681 nonn,base,easy
%O A037681 1,2
%A A037681 _Clark Kimberling_