%I #21 Dec 14 2023 05:39:13
%S 2,21,213,2132,21321,213213,2132132,21321321,213213213,2132132132,
%T 21321321321,213213213213,2132132132132,21321321321321,
%U 213213213213213,2132132132132132
%N Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,1,3.
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (10,0,1,-10).
%F G.f.: x*(2+x+3*x^2) / ( (x-1)*(10*x-1)*(1+x+x^2) ). - _R. J. Mathar_, Nov 21 2011
%t Table[FromDigits[PadRight[{},n,{2,1,3}]],{n,20}] (* or *) LinearRecurrence[{10,0,1,-10},{2,21,213,2132},20] (* _Harvey P. Dale_, Jun 23 2016 *)
%o (PARI) Vec(x*(2+x+3*x^2)/((x-1)*(10*x-1)*(1+x+x^2)) + O(x^25)) \\ _Jinyuan Wang_, Apr 14 2020
%K nonn,base,easy
%O 1,1
%A _Clark Kimberling_