A086945 a(n) = 7*10^n - 9.

61, 691, 6991, 69991, 699991, 6999991, 69999991, 699999991, 6999999991, 69999999991, 699999999991, 6999999999991, 69999999999991, 699999999999991, 6999999999999991, 69999999999999991, 699999999999999991, 6999999999999999991, 69999999999999999991

Offset: 1

Author

Ray Chandler, Jul 24 2003

Keywords

• nonn
• base
• easy

Comments

a(n) = k where R(k+9) = 7.

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..300
• Index entries for linear recurrences with constant coefficients, signature (11,-10).

Crossrefs

Cf. A004086, A086940.

Programs

Magma

[7*10^n-9: n in [1..25] ]; // Vincenzo Librandi, Aug 22 2011

Mathematica

Table[10 FromDigits[PadRight[{6},n,9]]+1,{n,20}] (* Harvey P. Dale, Aug 14 2021 *)

Formula

R(a(n)) = A086940(n).

From Elmo R. Oliveira, Apr 30 2025: (Start)

G.f.: x*(20*x+61)/((x-1)*(10*x-1)).

E.g.f.: 2 - 9*exp(x) + 7*exp(10*x).

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