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%I #16 Mar 15 2024 02:23:25
%S 12,70,88,204,220,1750,1888,2958,8142,8632,9114,14664,18414,18762,
%T 20118,20712,25194,45520,64206,65652,65964,77814,79338,79824,85096,
%U 90804,103410,103644,117822,158946,163938,176364,185776,186612,194416,202656,203898,245632
%N Numbers k such that sigma(k) = 2*sigma(k+1).
%C The cases sigma(k) = 3*sigma(k+1) are rarer: k=180, 12000, 30996, 47940, ... [_R. J. Mathar_, Jul 25 2009]
%H Donovan Johnson, <a href="/A163193/b163193.txt">Table of n, a(n) for n = 1..1000</a>
%F {k: A000203(k) = 2*A000203(k+1)}.
%t f[n_]:=DivisorSigma[1,n]; lst={};Do[If[f[n]==f[n+1]*2,AppendTo[lst,n]], {n,9!}];lst
%Y Cf. A067081, A002961, A058073.
%K nonn
%O 1,1
%A _Vladimir Joseph Stephan Orlovsky_, Jul 22 2009
%E Edited by _R. J. Mathar_, Jul 25 2009