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%I #14 Aug 03 2014 14:37:26
%S 6,10,11,14,15,16,17,20,21,23,24,25,26,28,30,31,33,34,35,38,39,40,41,
%T 42,44,46,47,48,51,52,53,54,55,56,57,58,59,60,62,63,65,66,68,69,70,71,
%U 74,75,76,77,78,79,80,82,83,84,85,86,87,88,89,90,92,93,94
%N Numbers n such that sigma(n) = sigma(k) has solution for distinct numbers n and k.
%e 6 and 11 are in the sequence because sigma(6) = sigma(11) = 12.
%e 7 is not on the list because sigma(7) = 8 and there is no other integer for which sigma(n) = 8.
%t max = 9000; sigmaList = Table[DivisorSigma[1, n], {n, Prime[PrimePi[max]]}]; Select[Range[Floor[Sqrt[max]]], Count[sigmaList, sigmaList[[#]]] > 1 &] (* _Alonso del Arte_, Feb 06 2012 *)
%Y Cf. A066074, A158913, A000203.
%K nonn
%O 1,1
%A _Jaroslav Krizek_, Feb 03 2012
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