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A257410
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Values of n such that there are exactly 3 solutions to x^2 - y^2 = n with x > y >= 0.
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9
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45, 48, 63, 64, 72, 75, 80, 81, 99, 112, 117, 128, 147, 153, 171, 175, 176, 180, 200, 207, 208, 243, 245, 252, 261, 272, 275, 279, 300, 304, 324, 325, 333, 363, 368, 369, 387, 392, 396, 423, 425, 464, 468, 475, 477, 496, 507, 531, 539, 549, 575, 588, 592
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OFFSET
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1,1
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LINKS
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EXAMPLE
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45 is in the sequence because there are 3 solutions to x^2 - y^2 = 45, namely (x,y) = (7,2),(9,6),(23,22).
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MATHEMATICA
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r[n_] := Reduce[x^2 - y^2 == n && x > y >= 0, {x, y}, Integers]; Reap[For[n = 1, n < 600, n++, rn = r[n]; If[rn[[0]] === Or && Length[rn] == 3, Print[n]; Sow[n]]]][[2, 1]] (* Jean-François Alcover, Apr 22 2015 *)
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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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