%I #20 Mar 16 2023 07:16:34

%S 1,11,100,902,8119,73073,657658,5918924,53270317,479432855,4314895696,

%T 38834061266,349506551395,3145558962557,28310030663014,

%U 254790275967128,2293112483704153

%N Base 9 digits are, in order, the first n terms of the periodic sequence with initial period 1,2.

%H <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (9,1,-9).

%F a(n) = 9*a(n-1) + a(n-2) - 9*a(n-3).

%F G.f.: x*(1+2*x)/((1-9*x)*(1-x^2)). a(n) = (11*9^n+4*(-1)^n-15)/80. - _Bruno Berselli_, Jan 20 2011

%t Table[FromDigits[PadRight[{},n,{1,2}],9],{n,20}] (* or *) LinearRecurrence[ {9,1,-9},{1,11,100},20] (* _Harvey P. Dale_, Feb 15 2020 *)

%K nonn,base,easy

%O 1,2

%A _Clark Kimberling_