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URL: https://oeis.org/A162693

⇱ A162693 - OEIS

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A162693
Strictly positive numbers k such that 30*k/(30+k) are integers.
13
6, 15, 20, 30, 45, 60, 70, 120, 150, 195, 270, 420, 870
OFFSET
1,1
COMMENTS
The ansatz 30*k/(30+k)=j (any integer j) yields k=30*j/(30-j) which demonstrates that the sequence is finite if k>=0. - R. J. Mathar, Jul 13 2009
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
KEYWORD
nonn,fini,full
AUTHOR
EXTENSIONS
Edited by R. J. Mathar, Jul 13 2009
STATUS
approved