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%I #25 May 03 2019 02:59:23
%S 0,0,0,6,30,90,252,756,2268,6642,19602,58806,176904,530712,1592136,
%T 4780782,14351094,43053282,129146724,387440172,1162320516,3486843450,
%U 10460294154,31380882462,94143001680,282429005040,847287015120,2541864234006,7625599079310
%N Number of strings over Z_3 of length n with trace 0 and subtrace 1.
%C Same as number of strings over GF(3) of length n with trace 0 and subtrace 1.
%H Max Alekseyev, <a href="http://home.gwu.edu/~maxal/gpscripts/">PARI/GP scripts for miscellaneous math problems</a>
%H F. Ruskey, <a href="http://combos.org/TSstringZ3">Strings over Z_3 with given trace and subtrace</a>
%H F. Ruskey, <a href="http://combos.org/TSstringF3">Strings over GF(3) with given trace and subtrace</a>
%H <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (6,-15,27,-36,27).
%F a(n; t, s) = a(n-1; t, s) + a(n-1; t+2, s+2t+1) + a(n-1; t+1, s+t+1) where t is the trace and s is the subtrace.
%F G.f.: -6q^4(q-1)/[(1-3q)(1+3q^2)(1-3q+3q^2)]. - Lawrence Sze, Oct 24 2004
%Y Cf. A073947, A073949, A073950, A073951, A073952.
%K easy,nonn
%O 1,4
%A _Frank Ruskey_ and Nate Kube, Aug 15 2002
%E Terms a(21) onward from _Max Alekseyev_, Apr 09 2013
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