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A162693
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Strictly positive numbers n such that 30*n/(30+n) are integers.
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13
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6, 15, 20, 30, 45, 60, 70, 120, 150, 195, 270, 420, 870
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OFFSET
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1,1
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COMMENTS
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The ansatz 30*n/(30+n)=j (any integer j) yields n=30*j/(30-j) which demonstrates that the sequence is finite if n>=0. [R. J. Mathar, Jul 13 2009]
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LINKS
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MATHEMATICA
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f[a_, b_]:=(a*b)/(a+b); a=30; lst={}; Do[If[f[a, n]==IntegerPart[f[a, n]], AppendTo[lst, n]], {n, 9!}]; lst
Select[Range[1000], IntegerQ[(30#)/(30+#)]&] (* Harvey P. Dale, Sep 25 2019 *)
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CROSSREFS
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KEYWORD
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nonn,fini,full
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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