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 A073997 #15 May 03 2019 07:17:48 %S A073997 1,2,3,16,76,272,1008,4096,16576,65792,261888,1048576,4197376, %T A073997 16781312,67104768,268435456,1073790976,4295032832,17179803648, %U A073997 68719476736,274878693376,1099512676352,4398045462528,17592186044416,70368756760576,281474993487872,1125899890065408,4503599627370496,18014398710808576 %N A073997 Number of strings of length n over GF(4) with trace 1 and subtrace 0. %C A073997 Same as the number of strings of length n over GF(4) with trace x and subtrace 0 where x=RootOf(z^2+z+1). Same as the number of strings of length n over GF(4) with trace y and subtrace 0 where y=1+x. %H A073997 F. Ruskey <a href="http://combos.org/TSstringF4">Strings over GF(4) with given trace and subtrace</a> %F A073997 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 A073997 G.f.: -(2*q^3-3*q^2+4*q-1)*q/[(1-2q)(1-4q)(1+4q^2)]. - Lawrence Sze, Oct 24 2004 %Y A073997 Cf. A073995, A073996, A073998, A073999, A074000. %K A073997 easy,nonn %O A073997 1,2 %A A073997 _Frank Ruskey_ and Nate Kube, Aug 16 2002 %E A073997 More terms from _Max Alekseyev_, Apr 16 2013