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A073995
Number of strings of length n over GF(4) with trace 0 and subtrace 0.
9
1, 1, 7, 28, 76, 256, 1072, 4288, 16576, 65536, 262912, 1051648, 4197376, 16777216, 67121152, 268484608, 1073790976, 4294967296, 17180065792, 68720263168, 274878693376, 1099511627776, 4398049656832, 17592198627328, 70368756760576, 281474976710656, 1125899957174272, 4503599828697088, 18014398710808576
OFFSET
1,3
FORMULA
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).
G.f.: -q*(26*q^3+5*q-1-13*q^2)/[(1-2q)(1-4q)(1+4q^2)]. - Lawrence Sze, Oct 24 2004
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Frank Ruskey and Nate Kube, Aug 16 2002
EXTENSIONS
More terms from Max Alekseyev, Apr 16 2013
STATUS
approved