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%I #18 Dec 14 2023 05:52:06
%S 1,12,121,1211,12112,121121,1211211,12112112,121121121,1211211211,
%T 12112112112,121121121121,1211211211211,12112112112112,
%U 121121121121121,1211211211211211
%N Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 1,2,1.
%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*(1+x)^2 / ( (x-1)*(10*x-1)*(1+x+x^2) ). - _R. J. Mathar_, Aug 12 2013
%o (PARI) Vec(x*(1+x)^2/((x-1)*(10*x-1)*(1+x+x^2)) + O(x^25)) \\ _Jinyuan Wang_, Apr 14 2020
%K nonn,base,easy
%O 1,2
%A _Clark Kimberling_
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