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A162693 Strictly positive numbers n such that 30*n/(30+n) are integers. 13
6, 15, 20, 30, 45, 60, 70, 120, 150, 195, 270, 420, 870 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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]

LINKS

Table of n, a(n) for n=1..13.

MATHEMATICA

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 *)

CROSSREFS

Cf. A162688, A162689, A162690, A162691, A162692

Cf. A127730. [From Franklin T. Adams-Watters, Aug 07 2009]

Sequence in context: A302022 A094183 A196394 * A056901 A208542 A012412

Adjacent sequences:  A162690 A162691 A162692 * A162694 A162695 A162696

KEYWORD

nonn,fini,full

AUTHOR

Vladimir Joseph Stephan Orlovsky, Jul 10 2009

EXTENSIONS

Edited by R. J. Mathar, Jul 13 2009

STATUS

approved

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Last modified September 26 20:36 EDT 2020. Contains 337374 sequences. (Running on oeis4.)