OFFSET
1,6
MATHEMATICA
a007691[m_] := Block[{f = 0, i = 1}, While[f < m, If[Divisible[DivisorSigma[1, i], i], ++f]; ++i; ]; Return[i - 1]]
a153800[n_] := Block[{i = 2, j, f = 0}, While[f < n, j = a007691[i]; If[PerfectNumberQ[j], ++f; ]; ++i]; Return[i - 1]]
a[n_] := a153800[n] - MersennePrimeExponent[n]
a /@ Range[1, 4] (* Julien Kluge, Dec 15 2016 *)
CROSSREFS
KEYWORD
more,nonn
AUTHOR
Omar E. Pol, Jan 13 2009
STATUS
approved