A162689 Strictly positive numbers n such that (18*n)/(18+n) are integers.

9, 18, 36, 63, 90, 144, 306

Offset

1,1

Comments

The 18th row of A127730.

The ansatz 18*n/(18+n)=j (any integer j) yields n=18*j/(18-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..7.

Mathematica

f[a_, b_]:=(a*b)/(a+b); a=18; lst={}; Do[If[f[a, n]==IntegerPart[f[a, n]], AppendTo[lst, n]], {n, 9!}]; lst
Select[Range[400], IntegerQ[(18#)/(18+#)]&] (* Harvey P. Dale, Nov 12 2011 *)

Crossrefs

Cf. A162688

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

Sequence in context: A234598 A051063 A173942 * A033896 A195332 A005010

Adjacent sequences: A162686 A162687 A162688 * A162690 A162691 A162692

Keyword

nonn,fini,full

Author

Vladimir Joseph Stephan Orlovsky, Jul 10 2009

Extensions

Edited by R. J. Mathar, Jul 13 2009

Status

approved