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A162690
Strictly positive numbers n such that 20*n/(20+n) are integers.
16
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]
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. A127730. [From Franklin T. Adams-Watters, Aug 07 2009]
Sequence in context: A005240 A147374 A080654 * A074219 A178612 A063133
KEYWORD
nonn,fini,full
AUTHOR
EXTENSIONS
Edited by R. J. Mathar, Jul 13 2009
STATUS
approved