A198973 a(n) = 8*10^n - 1.

7, 79, 799, 7999, 79999, 799999, 7999999, 79999999, 799999999, 7999999999, 79999999999, 799999999999, 7999999999999, 79999999999999, 799999999999999, 7999999999999999, 79999999999999999, 799999999999999999, 7999999999999999999, 79999999999999999999, 799999999999999999999

Offset: 0

Author

Vincenzo Librandi, Nov 02 2011

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 0..200
• Index entries for linear recurrences with constant coefficients, signature (11,-10).

Programs

Magma

[8*10^n-1 : n in [0..20]];

Mathematica

Table[FromDigits[PadRight[{7},n,9]],{n,20}] (* Harvey P. Dale, Jun 05 2012 *)
CoefficientList[Series[(7 + 2*x)/(1 - 11*x + 10*x^2), {x, 0, 30}], x] (* Vincenzo Librandi, Jan 04 2013 *)

Formula

a(n) = 10*a(n-1) + 9.

a(n) = 11*a(n-1) - 10*a(n-2), n>1.

G.f.: (7 + 2*x)/(1 - 11*x + 10*x^2). - Vincenzo Librandi, Jan 04 2013

E.g.f.: exp(x)*(8*exp(9*x) - 1). - Elmo R. Oliveira, Jun 10 2025