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A153803 a(n) = A153800(n) - A000043(n). 2
0, 0, 0, 0, 0, 2, 6, 10, 49, 103, 122, 167 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,6

LINKS

Table of n, a(n) for n=1..12.

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

Cf. A000040, A000043, A000668, A000225, A000396, A007691, A153800, A153801, A153802.

Sequence in context: A248784 A067868 A298760 * A083524 A222559 A095107

Adjacent sequences:  A153800 A153801 A153802 * A153804 A153805 A153806

KEYWORD

more,nonn

AUTHOR

Omar E. Pol, Jan 13 2009

STATUS

approved

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Last modified December 7 00:36 EST 2019. Contains 329812 sequences. (Running on oeis4.)