A177108 a(n) = 4*(10^n-3).

28, 388, 3988, 39988, 399988, 3999988, 39999988, 399999988, 3999999988, 39999999988, 399999999988, 3999999999988, 39999999999988, 399999999999988, 3999999999999988, 39999999999999988, 399999999999999988

Offset: 1

Author

Vincenzo Librandi, Nov 15 2010

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..200
• Index entries for linear recurrences with constant coefficients, signature (11,-10).

Programs

Magma

[4*(10^n-3): n in [1..20]]; // Vincenzo Librandi, Jul 15 2012

Mathematica

CoefficientList[Series[4*(7+20*x)/((10*x-1)*(x-1)),{x,0,40}],x] (* Vincenzo Librandi, Jul 15 2012 *)
4(10^Range[20]-3) (* or *) LinearRecurrence[{11,-10},{28,388},20] (* Harvey P. Dale, Sep 25 2012 *)

Formula

G.f.: 4*x*(7+20*x) / ( (10*x-1)*(x-1) ). a(n)=4*A173833(n). - R. J. Mathar, Jan 06 2011

a(n) = a(n-1) +36*10^(n-1) = 10*a(n-1) +108 = 11*a(n-1) -10*a(n-2). - Vincenzo Librandi, Jul 15 2012