A162693 Strictly positive numbers n such that 30*n/(30+n) are integers.

6, 15, 20, 30, 45, 60, 70, 120, 150, 195, 270, 420, 870

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 * A343893 A056901 A208542

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