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%I #8 Apr 03 2019 12:01:48
%S 1,9,73,592,4801,38935,315754,2560693,20766637,168412696,1365788605,
%T 11076234500,89825738954,728466283251,5907695633935,47910065991605,
%U 388539722685585,3150968653039294,25553638078006016,207234184444162395,1680622033979603605
%N Number of n-length words over a 9-ary alphabet {a_1,a_2,...,a_9} avoiding consecutive letters a_i, a_{i+1}.
%H Alois P. Heinz, <a href="/A277672/b277672.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (9,-8,7,-6,5,-4,3,-2,1)
%F G.f.: 1/(1 + Sum_{j=1..9} (10-j)*(-x)^j).
%p a:= proc(n) option remember; `if`(n<0, 0, `if`(n=0, 1,
%p -add((-1)^j*(10-j)*a(n-j), j=1..9)))
%p end:
%p seq(a(n), n=0..25);
%t 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 *)
%Y Column k=9 of A277666.
%K nonn,easy
%O 0,2
%A _Alois P. Heinz_, Oct 26 2016
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