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Smallest nonunitary multiperfect number of index n; i.e., smallest k such that sigma(k) - usigma(k) = nk.
5

%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