A037575 Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,1,2.

2, 21, 212, 2122, 21221, 212212, 2122122, 21221221, 212212212, 2122122122, 21221221221, 212212212212, 2122122122122, 21221221221221, 212212212212212, 2122122122122122

Offset

1,1

Links

Table of n, a(n) for n=1..16.

Index entries for linear recurrences with constant coefficients, signature (10,0,1,-10).

Formula

G.f.: x*(2+x+2*x^2) / ( (x-1)*(10*x-1)*(1+x+x^2) ). - R. J. Mathar, Nov 21 2011

Mathematica

LinearRecurrence[{10, 0, 1, -10}, {2, 21, 212, 2122}, 30] (* or *) Table[ FromDigits[ PadRight[{}, n, {2, 1, 2}]], {n, 30}] (* Harvey P. Dale, Dec 12 2014 *)

Prog

(PARI) Vec(x*(2+x+2*x^2)/((x-1)*(10*x-1)*(1+x+x^2)) + O(x^25)) \\ Jinyuan Wang, Apr 14 2020

Crossrefs

Sequence in context: A037495 A024763 A304272 * A305659 A008351 A037743

Adjacent sequences: A037572 A037573 A037574 * A037576 A037577 A037578

Keyword

nonn,base,easy

Author

Clark Kimberling

Status

approved