%I #20 Dec 14 2023 05:31:09
%S 2,21,213,2130,21302,213021,2130213,21302130,213021302,2130213021,
%T 21302130213,213021302130,2130213021302,21302130213021,
%U 213021302130213,2130213021302130,21302130213021302,213021302130213021,2130213021302130213,21302130213021302130
%N Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,1,3,0.
%H <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (10,0,0,1,-10).
%F a(n) = 10*a(n-1) + a(n-4) - 10*a(n-5). G.f.: x*(2+x+3*x^2) / ((x-1)*(10*x-1)*(1+x)*(x^2+1)). - _R. J. Mathar_, Oct 05 2009
%t nn=10;With[{c=PadLeft[{},4nn,{2,1,3,0}]},Table[FromDigits[Take[c,n]], {n,4nn}]] (* _Harvey P. Dale_, Aug 16 2011 *)
%o (PARI) Vec(x*(2+x+3*x^2)/((x-1)*(10*x-1)*(1+x)*(x^2+1)) + O(x^25)) \\ _Jinyuan Wang_, Apr 14 2020
%K nonn,base,easy
%O 1,1
%A _Clark Kimberling_
%E More terms from _Harvey P. Dale_, Aug 16 2011