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A073948
Number of strings over Z_3 of length n with trace 0 and subtrace 1.
5
0, 0, 0, 6, 30, 90, 252, 756, 2268, 6642, 19602, 58806, 176904, 530712, 1592136, 4780782, 14351094, 43053282, 129146724, 387440172, 1162320516, 3486843450, 10460294154, 31380882462, 94143001680, 282429005040, 847287015120, 2541864234006, 7625599079310
OFFSET
1,4
COMMENTS
Same as number of strings over GF(3) of length n with trace 0 and subtrace 1.
FORMULA
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.
G.f.: -6q^4(q-1)/[(1-3q)(1+3q^2)(1-3q+3q^2)]. - Lawrence Sze, Oct 24 2004
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Frank Ruskey and Nate Kube, Aug 15 2002
EXTENSIONS
Terms a(21) onward from Max Alekseyev, Apr 09 2013
STATUS
approved