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0, 1 and all numbers >= 9.
1

%I #19 Mar 19 2023 10:42:41

%S 0,1,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,

%T 31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,

%U 54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77

%N 0, 1 and all numbers >= 9.

%C Used to illustrate Besicovitch's density theorem.

%D H. Halberstam and K. F. Roth, Sequences, Oxford, 1966; see p. 6.

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).

%F G.f.: x^2*(1+7*x-7*x^2)/(1-x)^2. - _Bruno Berselli_, Sep 02 2011

%t Complement[Range[0,100],Range[2,8]] (* _Harvey P. Dale_, Oct 10 2014 *)

%o (PARI) a(n)=if(n>2,n+6,n-1) \\ _Charles R Greathouse IV_, Sep 02 2011

%K nonn,easy

%O 1,3

%A _N. J. A. Sloane_, Oct 19 2010