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A277672
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Number of n-length words over a 9-ary alphabet {a_1,a_2,...,a_9} avoiding consecutive letters a_i, a_{i+1}.
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2
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1, 9, 73, 592, 4801, 38935, 315754, 2560693, 20766637, 168412696, 1365788605, 11076234500, 89825738954, 728466283251, 5907695633935, 47910065991605, 388539722685585, 3150968653039294, 25553638078006016, 207234184444162395, 1680622033979603605
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OFFSET
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0,2
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LINKS
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FORMULA
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G.f.: 1/(1 + Sum_{j=1..9} (10-j)*(-x)^j).
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MAPLE
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a:= proc(n) option remember; `if`(n<0, 0, `if`(n=0, 1,
-add((-1)^j*(10-j)*a(n-j), j=1..9)))
end:
seq(a(n), n=0..25);
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MATHEMATICA
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LinearRecurrence[{9, -8, 7, -6, 5, -4, 3, -2, 1}, {1, 9, 73, 592, 4801, 38935, 315754, 2560693, 20766637}, 30] (* Harvey P. Dale, Apr 03 2019 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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