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%I #31 Feb 17 2024 10:30:31
%S 2,21,212,2121,21212,212121,2121212,21212121,212121212,2121212121,
%T 21212121212,212121212121,2121212121212,21212121212121,
%U 212121212121212,2121212121212121
%N Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,1.
%H Vincenzo Librandi, <a href="/A037495/b037495.txt">Table of n, a(n) for n = 1..1000</a>
%H <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (10,1,-10).
%F G.f.: x*(2+x) / ((x-1)*(10*x-1)*(1+x)). - _R. J. Mathar_, Nov 21 2011
%t Table[-(1/6)-(1/22)*(-1)^n+(7/33)*10^n,{n,1,20}] (* _Vincenzo Librandi_, Nov 23 2011 *)
%t Table[FromDigits[PadRight[{},n,{2,1}]],{n,20}] (* _Harvey P. Dale_, Aug 21 2013 *)
%o (Magma) [-(1/6)-(1/22)*(-1)^n+(7/33)*10^n: n in [1..20]]; // _Vincenzo Librandi_, Nov 23 2011
%K nonn,easy,base
%O 1,1
%A _Clark Kimberling_