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A132583 a(n) = n 2's sandwiched between two 1's. 3
11, 121, 1221, 12221, 122221, 1222221, 12222221, 122222221, 1222222221, 12222222221, 122222222221, 1222222222221, 12222222222221, 122222222222221, 1222222222222221, 12222222222222221, 122222222222222221 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,1

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..500

Index entries for linear recurrences with constant coefficients, signature (11, -10).

FORMULA

a(0) = 11; a(n) = 10*a(n-1) + 11. - Jonathan Vos Post, Nov 24 2007 [corrected by Jon E. Schoenfield, Jan 28 2018]

O.g.f.: 11/((-1+x)*(-1+10*x)) = -(110/9)/(-1+10*x)+(11/9)/(-1+x). - R. J. Mathar, Nov 28 2007

a(n) = 20*(10^n-1)/9 + 10^(n+1)+1, with n>=0. - Paolo P. Lava, Dec 19 2007

MAPLE

g:=(1+z)/((1-z)*(1-10*z)): gser:=series(g, z=0, 43): seq((coeff(gser, z, n))-1, n=1..24); # Zerinvary Lajos, Feb 25 2009

MATHEMATICA

NestList[10#+11&, 11, 20] (* or *) LinearRecurrence[{11, -10}, {11, 121}, 20] (* Harvey P. Dale, Sep 24 2012 *)

PROG

(MAGMA) [20*(10^n-1)/9+10^(n+1)+1: n in [0..25]]; // Vincenzo Librandi, Aug 10 2011

CROSSREFS

Sequence in context: A106473 A125315 A223676 * A007907 A171285 A216132

Adjacent sequences:  A132580 A132581 A132582 * A132584 A132585 A132586

KEYWORD

nonn,base,easy

AUTHOR

Paul Curtz, Nov 21 2007

STATUS

approved

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Last modified December 6 10:24 EST 2021. Contains 349563 sequences. (Running on oeis4.)