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A047697
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Smallest positive number that can be written in n ways as a sum of two (not necessarily positive) coprime cubes.
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1
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OFFSET
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1,2
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REFERENCES
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R. K. Guy, Unsolved Problems in Number Theory, Section D1.
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LINKS
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MATHEMATICA
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(* This naive program is not convenient for more than 4 terms *) max = 300; Clear[k]; k[_] = 0; t = Reap[ Do[ Do[z = x^3 + y^3; If[CoprimeQ[x, y], k[z] = k[z] + 1]; z = -x^3 + y^3; If[CoprimeQ[x, y], k[z] = k[z] + 1]; kz = k[z]; If[kz > 1, Sow[{z, kz}]], {y, x, max}], {x, 1, max}]][[2, 1]]; s = Sort[t]; a[n_] := Select[s, #[[2]] == n &, 1][[1, 1]]; a[1] = 1; Table[a[n], {n, 1, 4}] (* Jean-François Alcover, Jan 11 2013 *)
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CROSSREFS
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KEYWORD
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nonn,nice,hard
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AUTHOR
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STATUS
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approved
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