A162692 - OEIS

%I #4 Mar 31 2012 12:38:25

%S 21,28,70,84,168,364,756

%N Strictly positive numbers n such that 28*n/(28+n) are integers.

%C The 28th row of A127730.

%C The ansatz 28*n/(28+n)=j (any integer j) yields n=28*j/(28-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=28;lst={};Do[If[f[a,n]==IntegerPart[f[a,n]],AppendTo[lst,n]],{n,9!}];lst

%Y Cf. A162688, A162689, A162690, A162691

%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