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%I #6 Oct 26 2016 11:38:55
%S 1,7,43,264,1621,9953,61112,375231,2303939,14146313,86859145,
%T 533319959,3274614074,20106311704,123453866991,758013577995,
%U 4654245334143,28577324020619,175466351588409,1077373112945523,6615130559166437,40617267861064920,249392273325801363
%N Number of n-length words over a 7-ary alphabet {a_1,a_2,...,a_7} avoiding consecutive letters a_i, a_{i+1}.
%H Alois P. Heinz, <a href="/A277670/b277670.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (7,-6,5,-4,3,-2,1)
%F G.f.: 1/(1 + Sum_{j=1..7} (8-j)*(-x)^j).
%p a:= proc(n) option remember; `if`(n<0, 0, `if`(n=0, 1,
%p -add((-1)^j*(8-j)*a(n-j), j=1..7)))
%p end:
%p seq(a(n), n=0..25);
%Y Column k=7 of A277666.
%K nonn,easy
%O 0,2
%A _Alois P. Heinz_, Oct 26 2016
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