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A131970 1 followed by 2n 2's. 1
1, 122, 12222, 1222222, 122222222, 12222222222, 1222222222222, 122222222222222, 12222222222222222, 1222222222222222222, 122222222222222222222, 12222222222222222222222 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..200

FORMULA

a(n)=2*(10^(2*n)-1)/9+10^(2*n), with n>=0. - Paolo P. Lava, Dec 19 2007

From Chai Wah Wu, Jun 17 2020: (Start)

a(n) = 101*a(n-1) - 100*a(n-2) for n > 1.

G.f.: (21*x + 1)/((x - 1)*(100*x - 1)). (End)

MATHEMATICA

NestList[FromDigits[PadRight[IntegerDigits[#], IntegerLength[#]+2, 2]]&, 1, 20]  (* Harvey P. Dale, Mar 06 2011 *)

Table[FromDigits[PadRight[{1}, 2n+1, 2]], {n, 0, 20}] (* Harvey P. Dale, Jul 30 2020 *)

PROG

(MAGMA) [2*(10^(2*n)-1)/9+10^(2*n): n in [0..15]]; // Vincenzo Librandi, Aug 10 2011

CROSSREFS

Sequence in context: A275502 A275399 A275264 * A233096 A121916 A097843

Adjacent sequences:  A131967 A131968 A131969 * A131971 A131972 A131973

KEYWORD

nonn,base,easy

AUTHOR

Paul Curtz, Oct 06 2007

STATUS

approved

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Last modified August 5 18:00 EDT 2021. Contains 346488 sequences. (Running on oeis4.)