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 A053411 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. 11
 1, 1, 5, 9, 13, 21, 29, 37, 49, 69, 81, 97, 113, 137, 149, 177, 197, 225, 253, 293, 317, 349, 377, 421, 441, 489, 529, 577, 613, 665, 709, 749, 797, 861, 901, 973, 1009, 1085, 1129, 1201, 1257, 1313, 1373, 1457, 1517, 1597, 1653, 1741, 1793, 1885, 1961 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 COMMENTS a(n)/(n/2)^2 -> Pi. LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 MATHEMATICA 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 *) CROSSREFS Cf. A053414, A053415, A053416, A053417. Bisections: A000328 and A036704. Sequence in context: A089217 A166049 A334214 * A332571 A023382 A314793 Adjacent sequences: A053408 A053409 A053410 * A053412 A053413 A053414 KEYWORD easy,nonn AUTHOR Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Jan 10 2000 STATUS approved

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Last modified September 21 17:55 EDT 2023. Contains 365503 sequences. (Running on oeis4.)