cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A162693 Strictly positive numbers n such that 30*n/(30+n) are integers.

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%I A162693 #6 Sep 25 2019 11:00:23
%S A162693 6,15,20,30,45,60,70,120,150,195,270,420,870
%N A162693 Strictly positive numbers n such that 30*n/(30+n) are integers.
%C A162693 The 30th row of A127730.
%C A162693 The ansatz 30*n/(30+n)=j (any integer j) yields n=30*j/(30-j) which demonstrates that the sequence is finite if n>=0. [R. J. Mathar, Jul 13 2009]
%t A162693 f[a_,b_]:=(a*b)/(a+b); a=30;lst={};Do[If[f[a,n]==IntegerPart[f[a,n]],AppendTo[lst,n]],{n,9!}];lst
%t A162693 Select[Range[1000],IntegerQ[(30#)/(30+#)]&] (* _Harvey P. Dale_, Sep 25 2019 *)
%Y A162693 Cf. A162688, A162689, A162690, A162691, A162692
%Y A162693 Cf. A127730. [From _Franklin T. Adams-Watters_, Aug 07 2009]
%K A162693 nonn,fini,full
%O A162693 1,1
%A A162693 _Vladimir Joseph Stephan Orlovsky_, Jul 10 2009
%E A162693 Edited by _R. J. Mathar_, Jul 13 2009