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A073953
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Number of strings over Z_4 of length n with trace 0 and subtrace 0.
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10
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OFFSET
| 1,2
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COMMENTS
| a(n; 0,0) where a(n; t,s) is the number of length n 4-ary strings whose digits sum to t mod 4 and whose sum of products of all pairs of digits sum to s mod 4.
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LINKS
| F. Ruskey, Strings over Z_4 of given Trace and Subtrace
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FORMULA
| a(n; t, s) = a(n-1; t, s) + a(n-1; t+3, s+3t+1) + a(n-1; t+2, s+2t) + a(n-1; t+1, s+t+1) where t is the trace and s is the subtrace.
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EXAMPLE
| a(3;0,0)=4 since the four 4-ary strings of trace 0, subtrace 0 and length 3 are { 000, 022, 202, 220 }.
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CROSSREFS
| Cf. A068711, A073955, A068777, A068786, A068778, A073959, A068788, A068789, A073962.
Sequence in context: A058816 A018446 A068620 * A206850 A094333 A018473
Adjacent sequences: A073950 A073951 A073952 * A073954 A073955 A073956
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KEYWORD
| easy,nonn
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AUTHOR
| Frank Ruskey and Nate Kube (ruskey(AT)cs.uvic.ca), Aug 15 2002
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EXTENSIONS
| Edited by N. J. A. Sloane (njas(AT)research.att.com) at the suggestion of Andrew Plewe, May 19 2007
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