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 A073998 #15 May 03 2019 07:17:51
%S A073998 0,2,7,16,60,272,1072,4096,16320,65792,262912,1048576,4193280,
%T A073998 16781312,67121152,268435456,1073725440,4295032832,17180065792,
%U A073998 68719476736,274877644800,1099512676352,4398049656832,17592186044416,70368739983360,281474993487872,1125899957174272,4503599627370496,18014398442373120
%N A073998 Number of strings of length n over GF(4) with trace 1 and subtrace 1.
%C A073998 Same as the number of strings of length n over GF(4) with trace x and subtrace y where x=RootOf(z^2+z+1) and y=1+x. Same as the number of strings of length n over GF(4) with trace y and subtrace x.
%H A073998 F. Ruskey <a href="http://combos.org/TSstringF4">Strings over GF(4) with given trace and subtrace</a>
%F A073998 a(n; t, s) = a(n-1; t, s) + a(n-1; t-1, s-(t-1)) + a(n-1; t-2, s-2(t-2)) + a(n-1; t-3, s-3(t-3)) where t is the trace and s is the subtrace. Note that all operations involving operands t or s are carried out over GF(4).
%F A073998 G.f.: -(2*q^2+5*q-2)*q^2/[(1-2q)(1-4q)(1+4q^2)]. - Lawrence Sze, Oct 24 2004
%e A073998 a(2; x,y)=2 since the two 4-ary strings of trace x, subtrace y and length 2 are { 1y, y1 }.
%Y A073998 Cf. A073995, A073996, A073997, A073999, A074000.
%K A073998 easy,nonn
%O A073998 1,2
%A A073998 _Frank Ruskey_ and Nate Kube, Aug 16 2002
%E A073998 More terms from _Max Alekseyev_, Apr 16 2013