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%I #7 Nov 21 2013 12:49:39
%S 9,18,36,63,90,144,306
%N Strictly positive numbers n such that (18*n)/(18+n) are integers.
%C The 18th row of A127730.
%C 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]
%t 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
%t Select[Range[400],IntegerQ[(18#)/(18+#)]&] (* _Harvey P. Dale_, Nov 12 2011 *)
%Y Cf. A162688
%Y Cf. A127730. [From _Franklin T. Adams-Watters_, Aug 07 2009]
%K nonn,fini,full
%O 1,1
%A _Vladimir Joseph Stephan Orlovsky_, Jul 10 2009
%E Edited by _R. J. Mathar_, Jul 13 2009