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%I #31 Jan 18 2024 06:36:47
%S 0,7,77,721,6545,59017,531377,4782841,43046465,387419977,3486783377,
%T 31381057561,282429532385,2541865820137,22876792438577,
%U 205891132061881,1853020188786305,16677181699535497,150094635296736977,1350851717672467801
%N a(n) = 9^n - 2^n.
%C a(n) is the number of words of length n over the alphabet {1,2,...,9} where at least one letter >= 3 appears. - _Joerg Arndt_, Jan 18 2024
%H Vincenzo Librandi, <a href="/A191465/b191465.txt">Table of n, a(n) for n = 0..300</a>
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-18).
%F a(n) = 11*a(n-1) - 18*a(n-2).
%F G.f.: 7*x/((1-2*x)*(1-9*x)). - _Vincenzo Librandi_, Oct 04 2014
%F a(n) = 7*A016133(n-1). - _R. J. Mathar_, Mar 10 2022
%t Table[9^n-2^n,{n,0,20}] (* _Harvey P. Dale_, Apr 16 2014 *)
%o (PARI) a(n)=9^n-1<<n \\ _Charles R Greathouse IV_, Jun 08 2011
%Y Cf. A118004, A016185.
%K nonn,easy
%O 0,2
%A _Vincenzo Librandi_, Jun 03 2011
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