A137466 1 concatenated with n 21's.

1, 121, 12121, 1212121, 121212121, 12121212121, 1212121212121, 121212121212121, 12121212121212121, 1212121212121212121, 121212121212121212121, 12121212121212121212121, 1212121212121212121212121, 121212121212121212121212121, 12121212121212121212121212121

Offset

0,2

Links

Vincenzo Librandi, Table of n, a(n) for n = 0..100

Index entries for linear recurrences with constant coefficients, signature (101,-100).

Formula

From Colin Barker, May 31 2015: (Start)

a(n) = (2^(3+2*n)*5^(1+2*n)-7)/33.

a(n) = 100*a(n-1) + 21.

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

G.f.: (20*x+1) / ((x-1)*(100*x-1)).

(End)

Example

a(7) = 1 21 21 21 21 21 21 21.

Mathematica

Table[FromDigits[PadRight[{1}, n, {1, 2}]], {n, 1, 31, 2}] (* or *) LinearRecurrence[{101, -100}, {1, 121}, 30] (* Harvey P. Dale, Aug 17 2013 *)

Prog

(PARI) Vec((20*x+1)/((x-1)*(100*x-1)) + O(x^30)) \\ Colin Barker, May 31 2015

Crossrefs

Sequence in context: A054319 A006061 A079215 * A062689 A057139 A321687

Adjacent sequences: A137463 A137464 A137465 * A137467 A137468 A137469

Keyword

easy,nonn,base

Author

Ctibor O. Zizka, Apr 19 2008

Extensions

More terms from Harvey P. Dale, Aug 17 2013

Status

approved