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Search: id:A162693
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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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+0
14
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| 6, 15, 20, 30, 45, 60, 70, 120, 150, 195, 270, 420, 870
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The 30th row of A127730.
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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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
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CROSSREFS
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Cf. A162688, A162689, A162690, A162691, A162692
Cf. A127730. [From Franklin T. Adams-Watters (FrankTAW(AT)Netscape.net), Aug 07 2009]
Sequence in context: A020886 A093508 A094183 this_sequence A056901 A012412 A009092
Adjacent sequences: A162690 A162691 A162692 this_sequence A162694 A162695 A162696
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KEYWORD
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nonn,fini,full
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AUTHOR
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Vladimir Orlovsky (4vladimir(AT)gmail.com), Jul 10 2009
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EXTENSIONS
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Edited by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jul 13 2009
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