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.

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, 76, 81, 87, 93, 100, 106, 112, 119, 126, 134, 141, 148, 156, 164, 173, 181, 189, 198, 207, 217, 226, 235, 245, 255, 266, 276, 286, 297, 308, 320, 331, 342, 354, 366, 379, 391, 403, 416

Offset

0,4

Links

Table of n, a(n) for n=0..63.

Index entries for linear recurrences with constant coefficients, signature (2,-1,0,0,1,-2,1)

Formula

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

Maple

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;

Crossrefs

Sequence in context: A026453 A026455 A082984 * A253083 A108130 A195060

Adjacent sequences: A085714 A085715 A085716 * A085718 A085719 A085720

Keyword

nonn,easy

Author

N. J. A. Sloane, Jul 20 2003

Status

approved