OFFSET
0,2
COMMENTS
Conjecture: this is also the number of integers from 0 to 10^n - 1 that lack 0, 1 and 2 as a digit.
Number of monic irreducible polynomials of degree 1 in GF(7)[x1,...,xn]. - Max Alekseyev, Jan 23 2006
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..500
Index entries for linear recurrences with constant coefficients, signature (8,-7).
FORMULA
a(n) = (7^(n+1) - 7) / 6. - Max Alekseyev, Jan 23 2006
a(n) = a(n-1) + 7^n with a(0)=0. - Vincenzo Librandi, Nov 13 2010
From Colin Barker, Jul 25 2014: (Start)
a(n) = 8*a(n-1) - 7*a(n-2).
G.f.: 7*x / ((x-1)*(7*x-1)). (End)
E.g.f.: (7/6)*(exp(7*x) - exp(x)). - G. C. Greubel, Jun 09 2021
MAPLE
a:=n->sum (7^j, j=1..n): seq(a(n), n=0..30); # Zerinvary Lajos, Oct 03 2007
MATHEMATICA
RecurrenceTable[{a[n]==7*a[n-1]+7, a[0]==0}, a, {n, 0, 30}] (* Vaclav Kotesovec, Jul 25 2014 *)
PROG
(PARI) concat(0, Vec(7*x/((x-1)*(7*x-1)) + O(x^30))) \\ Colin Barker, Jul 25 2014
(Magma) [(7/6)*(7^n -1): n in [0..30]]; // G. C. Greubel, Jun 09 2021
(Sage) [(7/6)*(7^n -1) for n in (0..30)] # G. C. Greubel, Jun 09 2021
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Alexandre Wajnberg, Apr 24 2005
STATUS
approved