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A226355
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Number of ordered pairs (i,j) with |i| * |j| <= n.
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4
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1, 9, 21, 33, 49, 61, 81, 93, 113, 129, 149, 161, 189, 201, 221, 241, 265, 277, 305, 317, 345, 365, 385, 397, 433, 449, 469, 489, 517, 529, 565, 577, 605, 625, 645, 665, 705, 717, 737, 757, 793, 805, 841, 853, 881, 909, 929, 941, 985, 1001, 1029, 1049, 1077, 1089, 1125, 1145, 1181
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OFFSET
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0,2
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LINKS
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FORMULA
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a(n) = 1 + 4n + 4*Sum_{k=1..n} tau(k), where tau(k) is the number of divisors of k. - Lorenz H. Menke, Jr., Mar 15 2016
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MAPLE
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MATHEMATICA
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f[n_] := Length[Complement[Union[Flatten[Table[If[Abs[i]*Abs[j] ≤ n, {i, j}], {i, -n, n}, {j, -n, n}], 1]], {Null}]]; Table[f[n], {n, 0, 100}]
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PROG
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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