

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
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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(n1) + 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^n1)/9 + 10^(n+1)+1, with n>=0.  Paolo P. Lava, Dec 19 2007


MAPLE

g:=(1+z)/((1z)*(110*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^n1)/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



