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A162689
Strictly positive numbers n such that (18*n)/(18+n) are integers.
17
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]
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. A127730. [From Franklin T. Adams-Watters, Aug 07 2009]
Sequence in context: A234598 A051063 A173942 * A033896 A195332 A005010
KEYWORD
nonn,fini,full
AUTHOR
EXTENSIONS
Edited by R. J. Mathar, Jul 13 2009
STATUS
approved