OFFSET
1,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 1..1000
Index entries for linear recurrences with constant coefficients, signature (8,-7).
FORMULA
a(n) = 2*(7^(n-1) - 1)/3 = 4*A023000(n-1).
a(n) = 7*a(n-1) + 4, with a(1)=0. - Vincenzo Librandi, Sep 30 2010
From G. C. Greubel, Aug 03 2019: (Start)
G.f.: 4*x^2/((1-x)*(1-7*x)).
E.g.f.: 2*(exp(7*x) - exp(x))/3. (End)
EXAMPLE
Base 7.................decimal
0.........................0
4.........................4
44.......................32
444.....................228
4444...................1600
44444.................11204
444444................78432
4444444..............549028
44444444............3843200
etc....................etc...
MAPLE
seq(4*(7^n-1)/6, n=0..21);
MATHEMATICA
2*(7^(Range[30]-1) -1)/3 (* G. C. Greubel, Aug 03 2019 *)
PROG
(PARI) vector(30, n, 2*(7^(n-1) -1)/3) \\ G. C. Greubel, Aug 03 2019
(Magma) [2*(7^(n-1) -1)/3: n in [1..30]]; // G. C. Greubel, Aug 03 2019
(Sage) [2*(7^(n-1) -1)/3 for n in (1..30)] # G. C. Greubel, Aug 03 2019
(GAP) List([1..30], n-> 2*(7^(n-1) -1)/3); # G. C. Greubel, Aug 03 2019
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Zerinvary Lajos, Feb 03 2007
EXTENSIONS
Terms a(21) onward added by G. C. Greubel, Aug 03 2019
STATUS
approved