OFFSET
0,2
COMMENTS
Number of 0..n arrays of 8 elements with zero second differences. - R. H. Hardin, Nov 16 2011
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (2,-1,0,0,0,0,1,-2,1).
FORMULA
G.f.: (1+x^7)/((1-x)^2*(1-x^7)).
a(n) = 2*a(n-1) -a(n-2) +a(n-7) -2*a(n-8) +a(n-9). - R. H. Hardin, Nov 16 2011
MAPLE
seq(coeff(series((1+x^7)/((1-x)^2*(1-x^7)), x, n+1), x, n), n = 0..70); # G. C. Greubel, Sep 12 2019
MATHEMATICA
CoefficientList[Series[(1+x^7)/(1-x)^2/(1-x^7), {x, 0, 70}], x] (* or *)
LinearRecurrence[{2, -1, 0, 0, 0, 0, 1, -2, 1}, {1, 2, 3, 4, 5, 6, 7, 10, 13}, 70] (* Harvey P. Dale, Dec 18 2012 *)
PROG
(PARI) a(n)=(n*(n+2)+[7, 11, 13, 13, 11, 7, 1][n%7+1])/7 \\ Charles R Greathouse IV, Nov 16 2011
(PARI) a(n)=(n*(n+2)+13-6*(n%7==6))\7 \\ Tani Akinari, Jul 25 2013
(Magma) R<x>:=PowerSeriesRing(Integers(), 70); Coefficients(R!( (1+x^7)/((1-x)^2*(1-x^7)) )); // G. C. Greubel, Sep 12 2019
(Sage)
def A008814_list(prec):
P.<x> = PowerSeriesRing(ZZ, prec)
return P((1+x^7)/((1-x)^2*(1-x^7))).list()
A008814_list(70) # G. C. Greubel, Sep 12 2019
(GAP) a:=[1, 2, 3, 4, 5, 6, 7, 10, 13];; for n in [10..70] do a[n]:=2*a[n-1]-a[n-2]+a[n-7]-2*a[n-8]+a[n-9]; od; a; # G. C. Greubel, Sep 12 2019
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
EXTENSIONS
More terms added by G. C. Greubel, Sep 12 2019
STATUS
approved