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%I #16 Aug 22 2019 08:42:10
%S 1,13,181,121679,1033474069
%N a(n) is smallest x such that sigma(phi(x))/sigma(x) = n.
%C A023199(6) < a(6) <= 1794819234390989. - _Donovan Johnson_, Oct 24 2011
%t a[ n_ ] := For[ x=1, True, x++, If[ DivisorSigma[ 1, EulerPhi[ x ] ]/DivisorSigma[ 1, x ]==n, Return[ x ] ] ]
%Y Cf. A023199, A033631, A066831, A067382, A067383, A067384, A197952.
%K nonn,more
%O 1,2
%A _Dean Hickerson_, Jan 20 2002
%E a(5) from _Vim Wenders_, Mar 11 2007
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