A125729 Numbers whose base 7 representation is 555....5.

0, 5, 40, 285, 2000, 14005, 98040, 686285, 4804000, 33628005, 235396040, 1647772285, 11534406000, 80740842005, 565185894040, 3956301258285, 27694108808000, 193858761656005, 1357011331592040, 9499079321144285

Offset: 1

Author

Zerinvary Lajos, Feb 02 2007

Keywords

• easy
• nonn

Examples

			Base 7.............decimal
0........................0
5........................5
55......................40
555....................285
5555..................2000
55555................14005
555555...............98040
5555555.............686285
55555555...........4804000
555555555.........33628005
etc....................etc...
		

Links

• Index entries for linear recurrences with constant coefficients, signature (8,-7).

Programs

Maple

seq(5*(7^n-1)/6, n=0..21);

Mathematica

Table[FromDigits[Table[5,n],7],{n,0,19}] (* James C. McMahon, Dec 21 2024 *)

Formula

a(n) = 5*(7^(n-1)-1)/6 = 5*A023000(n-1).

a(n) = 7*a(n-1) + 5 for n > 1. - Vincenzo Librandi, Sep 30 2010

G.f.: 5*x^2 / ( (7*x-1)*(x-1) ). - R. J. Mathar, Sep 30 2013