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 A073996 #19 May 03 2019 07:22:07
%S A073996 0,1,3,12,60,256,1008,4032,16320,65536,261888,1047552,4193280,
%T A073996 16777216,67104768,268419072,1073725440,4294967296,17179803648,
%U A073996 68719214592,274877644800,1099511627776,4398045462528,17592181850112,70368739983360,281474976710656,1125899890065408,4503599560261632,18014398442373120
%N A073996 Number of strings of length n over GF(4) with trace 0 and subtrace 1.
%C A073996 Same as the number of strings of length n over GF(4) with trace 0 and subtrace x where x=RootOf(z^2+z+1). Same as the number of strings of length n over GF(4) with trace 0 and subtrace y where y=1+x.
%H A073996 F. Ruskey <a href="http://combos.org/TSstringF4">Strings over GF(4) with given trace and subtrace</a>
%F A073996 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 A073996 G.f.: (6*q^2-3*q+1)*q^2/[(1-2q)(1-4q)(1+4q^2)]. - Lawrence Sze, Oct 24 2004
%e A073996 a(2;0,1)=1 since the one 4-ary string of trace 0, subtrace 1 and length 2 is { 11 }.
%t A073996 CoefficientList[Series[x^2 (6x^2-3x+1)/((1-2x)(1-4x)(1+4x^2)), {x,0,30}], x] (* _Harvey P. Dale_, Apr 03 2011 *)
%Y A073996 Cf. A073995, A073997, A073998, A073999, A074000.
%K A073996 easy,nonn
%O A073996 1,3
%A A073996 _Frank Ruskey_ and Nate Kube, Aug 16 2002
%E A073996 More terms from _Harvey P. Dale_, Apr 03 2011
%E A073996 More terms from _Max Alekseyev_, Apr 16 2013