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A277670
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Number of n-length words over a 7-ary alphabet {a_1,a_2,...,a_7} avoiding consecutive letters a_i, a_{i+1}.
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2
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1, 7, 43, 264, 1621, 9953, 61112, 375231, 2303939, 14146313, 86859145, 533319959, 3274614074, 20106311704, 123453866991, 758013577995, 4654245334143, 28577324020619, 175466351588409, 1077373112945523, 6615130559166437, 40617267861064920, 249392273325801363
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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..7} (8-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*(8-j)*a(n-j), j=1..7)))
end:
seq(a(n), n=0..25);
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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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