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A037638
Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,1,3.
0
2, 21, 213, 2132, 21321, 213213, 2132132, 21321321, 213213213, 2132132132, 21321321321, 213213213213, 2132132132132, 21321321321321, 213213213213213, 2132132132132132
OFFSET
1,1
FORMULA
G.f.: x*(2+x+3*x^2) / ( (x-1)*(10*x-1)*(1+x+x^2) ). - R. J. Mathar, Nov 21 2011
MATHEMATICA
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 *)
PROG
(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
CROSSREFS
Sequence in context: A305659 A008351 A037743 * A131698 A163068 A109684
KEYWORD
nonn,base,easy
STATUS
approved