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%I
%S 3,4,6,8,12,18,24,36,40,60,84,156,180,600
%N Numbers n such that n*sigma_0(n)/(n-sigma_0(n))= c, c an integer.
%C A000027(n)*A000005(n)/(A000027(n)-A000005(n))=c, c an integer.
%C No other term < 10000000. - _Michel Marcus_, Jun 02 2013
%t nsiQ[n_]:=Module[{s=DivisorSigma[0,n]},IntegerQ[(n*s)/(n-s)]]; Select[ Range[3,600],nsiQ] (* _Harvey P. Dale_, Dec 05 2019 *)
%o (PARI) isok(n) = {nd = numdiv(n); type(n*nd/(n-nd)) == "t_INT"} \\ _Michel Marcus_, Jun 02 2013
%Y Cf. A000027, A000005
%K easy,nonn
%O 1,1
%A _Ctibor O. Zizka_, Nov 01 2008
%E Corrected and extended by _Michel Marcus_, Jun 02 2013
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