1,1

An upper bound for a(7) is a 77-digit number with factorization: 2^35 3^20 5^9 7^3 11 13^2 17 19 23 29 31 37^2 41 61 67 71 73 109 137 409 521 547 1093 36809 368089.

An upper bound for a(8) is a 165-digit number that can be found on given link where line begins with 25/3.

Table of n, a(n) for n=1..6.

Walter Nissen and Michel Marcus, Extended Table of Abundancies

a(1) = 3 because sigma(3)/3 = 4/3 = 1 + 1/3 and 3 is the earliest m such that sigma(m)/m = 1 + 1/3.

Cf. A160320, A088912.

Sequence in context: A132515 A279122 A246957 * A262541 A036300 A169815

Adjacent sequences: A216894 A216895 A216896 * A216898 A216899 A216900

nonn

Michel Marcus, Sep 19 2012

approved