A205085 a(n) = n 5's sandwiched between two 1's.

11, 151, 1551, 15551, 155551, 1555551, 15555551, 155555551, 1555555551, 15555555551, 155555555551, 1555555555551, 15555555555551, 155555555555551, 1555555555555551, 15555555555555551, 155555555555555551, 1555555555555555551, 15555555555555555551

Offset

0,1

Links

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

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

Formula

a(0)=11, a(n) = 10*a(n-1) + 41.

a(n) = (140*10^n - 41)/9 (see PARI code by Charles R Greathouse IV).

a(n) = 11*a(n-1) - 10*a(n-2). - Vincenzo Librandi, Jan 23 2012

Mathematica

a[0]=11; a[n_]:=a[n-1]*10+41; Table[a[n], {n, 0, 44}]
LinearRecurrence[{11, -10}, {11, 151}, 50] (* Vincenzo Librandi, Jan 23 2012 *)
Table[10FromDigits[PadRight[{1}, n, 5]]+1, {n, 20}] (* Harvey P. Dale, May 02 2019 *)

Prog

(PARI) a(n)=(140*10^n-41)/9 \\ Charles R Greathouse IV, Jan 23 2012
(Magma) I:=[11, 151]; [n le 2 select I[n] else 11*Self(n-1)-10*Self(n-2): n in [1..25]]; // Vincenzo Librandi, Jan 23 2012

Crossrefs

Sequence in context: A038141 A307072 A142083 * A068646 A176365 A077577

Adjacent sequences: A205082 A205083 A205084 * A205086 A205087 A205088

Keyword

nonn,base,easy,less

Author

José María Grau Ribas, Jan 22 2012

Status

approved