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 A085717 Consider the square lattice L and the sublattice K of index 5 spanned by (2,-1), (1,2); a(n) = number of points (x,y) in M with x >= 0, y >= 0, x+y <= n. 0

%I

%S 1,1,1,2,3,5,6,7,9,11,14,16,18,21,24,28,31,34,38,42,47,51,55,60,65,71,

%T 76,81,87,93,100,106,112,119,126,134,141,148,156,164,173,181,189,198,

%U 207,217,226,235,245,255,266,276,286,297,308,320,331,342,354,366,379,391,403,416

%N Consider the square lattice L and the sublattice K of index 5 spanned by (2,-1), (1,2); a(n) = number of points (x,y) in M with x >= 0, y >= 0, x+y <= n.

%H <a href="/index/Rec#order_07">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,0,0,1,-2,1)

%F G.f.: (x^3-x+1)/[(1-x^5)(1-x)^2].

%p a := proc(n) local i,t0,t1,t2; t0 := 0; for i from 0 to floor(2*n/5) do t1 := min(n-3*i,2*i); t2 := ceil(-i/2); t0 := t0+t1-t2+1; od; t0; end;

%K nonn,easy

%O 0,4

%A _N. J. A. Sloane_, Jul 20 2003

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Last modified September 22 13:48 EDT 2021. Contains 347607 sequences. (Running on oeis4.)