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%I #12 Oct 20 2022 23:07:30
%S 1,1,5,9,13,21,29,37,49,69,81,97,113,137,149,177,197,225,253,293,317,
%T 349,377,421,441,489,529,577,613,665,709,749,797,861,901,973,1009,
%U 1085,1129,1201,1257,1313,1373,1457,1517,1597,1653,1741,1793,1885,1961
%N Circle numbers (version 1): a(n)= number of points (i,j), i,j integers, contained in a circle of diameter n, centered at the origin.
%C a(n)/(n/2)^2 -> Pi.
%H G. C. Greubel, <a href="/A053411/b053411.txt">Table of n, a(n) for n = 0..1000</a>
%t a[n_] := (m = Ceiling[n/2]; Sum[Boole[i^2 + j^2 <= n^2/4], {i, -m, m}, {j, -Ceiling @ Sqrt[ m^2 - i^2 ], Ceiling @ Sqrt[ m^2 - i^2 ]}]); Table[a[n], {n, 0, 50}] (* _Jean-François Alcover_, Jun 06 2013 *)
%Y Cf. A053414, A053415, A053416, A053417.
%Y Bisections: A000328 and A036704.
%K easy,nonn
%O 0,3
%A Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Jan 10 2000