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

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

Offset: 1

Author

Vladimir Joseph Stephan Orlovsky, Jul 10 2009

Keywords

• nonn
• fini
• full

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]

Crossrefs

Cf. A162688

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

Programs

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 *)

Extensions

Edited by R. J. Mathar, Jul 13 2009