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%I #18 Feb 10 2014 04:02:18
%S 1,5,9,13,21,25,29,37,45,49,57,61,69,81,89,97,101,109,113,121,129,137,
%T 145,149,161,169,177,185,193,197,213,221,225,233,241,249,253,261,277,
%U 285,293,301,305,317,325,333,341,349,357,365,373,377,385,401,405,421
%N Number of points in square lattice covered by a disc centered at (0,0) as its radius increases.
%C Useful for rasterizing circles.
%C Conjecture: the number of lattice points in a quadrant of the disk is equal to A000592(n-1). - _L. Edson Jeffery_, Feb 10 2014
%D J. H. Conway and N. J. A. Sloane, "Sphere Packings, Lattices and Groups", Springer-Verlag, p. 106.
%H T. D. Noe, <a href="/A057961/b057961.txt">Table of n, a(n) for n=1..1000</a>
%H L. Edson Jeffery, <a href="/A057961/a057961.pdf">Illustration of first few terms</a>.
%e 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).
%t 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 *)
%Y Cf. A004018, A004020, A005883, A057962. Distinct terms of A057655.
%Y Cf. A000404, A001481, A232499.
%K easy,nonn
%O 1,2
%A _Ken Takusagawa_, Oct 15 2000
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