A162690 Strictly positive numbers n such that 20*n/(20+n) are integers.

5, 20, 30, 60, 80, 180, 380

Offset

1,1

Comments

The 20th row of A127730.

The ansatz 20*n/(20+n)=j (any integer j) yields n=20*j/(20-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=20; lst={}; Do[If[f[a, n]==IntegerPart[f[a, n]], AppendTo[lst, n]], {n, 9!}]; lst

Crossrefs

Cf. A162688, A162689

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

Sequence in context: A005240 A147374 A080654 * A074219 A178612 A063133

Adjacent sequences: A162687 A162688 A162689 * A162691 A162692 A162693

Keyword

nonn,fini,full

Author

Vladimir Joseph Stephan Orlovsky, Jul 10 2009

Extensions

Edited by R. J. Mathar, Jul 13 2009

Status

approved