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.
%I A162821 #7 Feb 21 2019 23:24:45
%S A162821 5,10,12,15,18,20,21,24,25,26,27,28,29,30,31,32,33,34,35,36,39,40,42,
%T A162821 45,48,50,55,60,66,75,80,90,105,120,130,180,210,255,330,480,930
%N A162821 Positive numbers k such that 30*k/(30-k) are integers.
%C A162821 The number k=30 is explicitly included, treating the result of division through zero as an integer.
%C A162821 Row 30 of A191973.
%p A162821 for m from 1 to 930 do if(m=30 or m*30 mod (m-30) = 0)then printf("%d, ", m): fi: od: # _Nathaniel Johnston_, Jun 22 2011
%t A162821 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
%Y A162821 Cf. A162688, A162689, A162690, A162691, A162692, A162693, A162694, A162817, A162818, A162819, A162820, A191973.
%K A162821 nonn,fini,full,easy
%O A162821 1,1
%A A162821 _Vladimir Joseph Stephan Orlovsky_, Jul 13 2009
%E A162821 Keywords fini,full added by _R. J. Mathar_, Jul 31 2009