%I #7 Jul 30 2017 22:41:44
%S 1,24,2520,186076800
%N Smallest nonunitary multiperfect number of index n; i.e., smallest k such that sigma(k) - usigma(k) = nk.
%C 4.5*10^14 < a(4) <= 1081895452249824576000.
%t nusigma[ n_ ] := DivisorSigma[ 1, n ]-Times@@(1+Power@@#&/@FactorInteger[ n ]); a[ n_ ] := For[ k=1, True, k++, If[ nusigma[ k ]==n k, Return[ k ] ] ]
%Y Cf. A048146, A064591, A064592, A064593, A064594, A064595.
%K nonn,hard,more
%O 0,2
%A _Dean Hickerson_, Sep 25 2001