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A051132
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Number of ordered pairs of integers (x,y) with x^2+y^2 < n^2.
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10
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0, 1, 9, 25, 45, 69, 109, 145, 193, 249, 305, 373, 437, 517, 609, 697, 793, 889, 1005, 1125, 1245, 1369, 1513, 1649, 1789, 1941, 2109, 2285, 2449, 2617, 2809, 2997, 3205, 3405, 3613, 3841, 4049, 4281, 4509, 4765, 5013, 5249, 5521, 5785, 6073, 6349, 6621
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OFFSET
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0,3
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COMMENTS
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LINKS
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EXAMPLE
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a(3)=25 from the points of shapes 00 (1), 10 (4), 11 (4), 20 (4), 21 (8), 22 (4).
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MATHEMATICA
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Table[Sum[SquaresR[2, k], {k, 0, n^2 - 1}], {n, 0, 46}]
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PROG
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(Haskell)
a051132 n = length [(x, y) | x <- [-n..n], y <- [-n..n], x^2 + y^2 < n^2]
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CROSSREFS
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Changing "<" to "<=" in the definition gives A000328.
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KEYWORD
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nonn,nice,easy
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AUTHOR
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Jostein Trondal (jostein.trondal(AT)protech.no)
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EXTENSIONS
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STATUS
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approved
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