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A037575 Decimal expansion of a(n) is given by the first n terms of the periodic sequence with initial period 2,1,2. 2
2, 21, 212, 2122, 21221, 212212, 2122122, 21221221, 212212212, 2122122122, 21221221221, 212212212212, 2122122122122, 21221221221221, 212212212212212, 2122122122122122 (list; graph; refs; listen; history; text; internal format)
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

a(n) = 10*a(n-1) + (1/9)*(2*(n mod 3) + 8*((n+1) mod 3) + 5*((n+2) mod 3)), with a(0)=0. - Paolo P. Lava, Jul 30 2009

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

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Last modified January 27 17:36 EST 2022. Contains 350611 sequences. (Running on oeis4.)