login
A125836
Numbers whose base 8 or octal representation is 555555555......5.
2
0, 5, 45, 365, 2925, 23405, 187245, 1497965, 11983725, 95869805, 766958445, 6135667565, 49085340525, 392682724205, 3141461793645, 25131694349165, 201053554793325, 1608428438346605, 12867427506772845, 102939420054182765
OFFSET
1,2
FORMULA
a(n) = 5*(8^(n-1) -1)/7 = 5*A023001(n-1).
a(n) = 8*a(n-1) + 5, with a(1)=0. - Vincenzo Librandi, Sep 30 2010
G.f.: 5*x^2/( (1-x)*(1-8*x)). - R. J. Mathar, Sep 30 2013
From G. C. Greubel, Aug 03 2019: (Start)
a(n) = 5*A024088(n-1)/7.
E.g.f.: 5*(exp(8*x) - exp(x))/7. (End)
EXAMPLE
Octal...............decimal
0........................0
5........................5
55......................45
555....................365
5555..................2925
55555................23405
555555..............187245
5555555............1497965
55555555..........11983725
555555555.........95869805
5555555555.......766958445
etc. ...............etc.
MAPLE
seq(5*(8^n-1)/7, n=0..30);
MATHEMATICA
5*(8^(Range[30]-1) -1)/7 (* G. C. Greubel, Aug 03 2019 *)
PROG
(PARI) vector(30, n, 5*(8^(n-1) -1)/7) \\ G. C. Greubel, Aug 03 2019
(Magma) [5*(8^(n-1) -1)/7: n in [1..30]]; // G. C. Greubel, Aug 03 2019
(Sage) [5*(8^(n-1) -1)/7 for n in (1..30)] # G. C. Greubel, Aug 03 2019
(GAP) List([1..30], n-> 5*(8^(n-1) -1)/7); # G. C. Greubel, Aug 03 2019
CROSSREFS
Sequence in context: A272494 A185009 A376525 * A001260 A088505 A067403
KEYWORD
easy,nonn
AUTHOR
Zerinvary Lajos, Feb 03 2007
STATUS
approved