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A277671
Number of n-length words over an 8-ary alphabet {a_1,a_2,...,a_8} avoiding consecutive letters a_i, a_{i+1}.
2
1, 8, 57, 406, 2892, 20600, 146736, 1045216, 7445184, 53032832, 377758463, 2690813426, 19166948203, 136528196220, 972504760052, 6927254109472, 49343562590512, 351479407373632, 2503624937520704, 17833584831080448, 127030508108889857, 904851724611169300
OFFSET
0,2
FORMULA
G.f.: 1/(1 + Sum_{j=1..8} (9-j)*(-x)^j).
MAPLE
a:= proc(n) option remember; `if`(n<0, 0, `if`(n=0, 1,
-add((-1)^j*(9-j)*a(n-j), j=1..8)))
end:
seq(a(n), n=0..25);
MATHEMATICA
LinearRecurrence[{8, -7, 6, -5, 4, -3, 2, -1}, {1, 8, 57, 406, 2892, 20600, 146736, 1045216}, 30] (* Harvey P. Dale, May 15 2018 *)
CROSSREFS
Column k=8 of A277666.
Sequence in context: A331792 A097114 A022038 * A015453 A181246 A281355
KEYWORD
nonn,easy
AUTHOR
Alois P. Heinz, Oct 26 2016
STATUS
approved