OFFSET
1,2
COMMENTS
Useful for rasterizing circles.
Conjecture: the number of lattice points in a quadrant of the disk is equal to A000592(n-1). - L. Edson Jeffery, Feb 10 2014
REFERENCES
J. H. Conway and N. J. A. Sloane, "Sphere Packings, Lattices and Groups", Springer-Verlag, p. 106.
LINKS
T. D. Noe, Table of n, a(n) for n=1..1000
L. Edson Jeffery, Illustration of first few terms.
EXAMPLE
a(2)=5 because (0,0); (0,1); (0,-1); (1,0); (-1,0) are covered by any disc of radius between 1 and sqrt(2).
MATHEMATICA
max = 100; A001481 = Select[Range[0, 4*max], SquaresR[2, #] != 0 &]; Table[SquaresR[2, A001481[[n]]], {n, 1, max}] // Accumulate (* Jean-François Alcover, Oct 04 2013 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Ken Takusagawa, Oct 15 2000
STATUS
approved