A177109 a(n) = 4*(10^n-5).

20, 380, 3980, 39980, 399980, 3999980, 39999980, 399999980, 3999999980, 39999999980, 399999999980, 3999999999980, 39999999999980, 399999999999980, 3999999999999980, 39999999999999980, 399999999999999980

Offset: 1

Author

Vincenzo Librandi, Nov 15 2010

Keywords

• nonn
• easy

Comments

Is this 20*A067272(n)?

Links

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

Crossrefs

Cf. A067272.

Programs

Maple

A177109:=n->4*(10^n-5): seq(A177109(n), n=1..30); # Wesley Ivan Hurt, Feb 16 2017

Mathematica

4(10^Range[20]-5) (* or *) LinearRecurrence[{11,-10},{20,380},20] (* Harvey P. Dale, Jul 26 2024 *)

Formula

G.f.: 20*x*(1+8*x) / ( (10*x-1)*(x-1) ). - R. J. Mathar, Jan 06 2011

a(n) = 11*a(n-1) - 10*a(n-2). - Wesley Ivan Hurt, Mar 17 2023