Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #23 Oct 28 2018 08:46:05
%S 4,3,2,12,10,8,4,2,7,56,78,8,2,2,32,16,4,2,532,152,136,8,68,31,992,
%T 128,8,64,32,16,4,8,128,32,8,2,43648,2528,32,4,2,32,2272,32,32,127,
%U 16256,32,32,4,536,8,32,8,52,16,32,41044,64,512,128,64,16,4,2,8
%N Abundance of A181595(n).
%C a(n) is a proper divisor of A181595(n).
%H Michel Marcus, <a href="/A181596/b181596.txt">Table of n, a(n) for n = 1..200</a>
%H Paul Pollack and Vladimir Shevelev, <a href="https://doi.org/10.1016/j.jnt.2012.06.008">On perfect and near-perfect numbers</a>, J. Number Theory 132 (2012), pp. 3037-3046. <a href="http://arxiv.org/abs/1011.6160">arXiv:1011.6160</a>
%F a(n) = A033880(A181595(n)).
%e Since A181595(1)=12, a(1)=sigma(12)-2*12=28-24=4.
%t Reap[For[n = 12, n <= 2 10^7, n++, abn = DivisorSigma[1, n] - 2n; If[1 < abn < n && Divisible[n, abn], Print[{n, abn}]; Sow[abn]]]][[2, 1]] (* _Jean-François Alcover_, Oct 28 2018 *)
%Y Cf. A181595, A000396, A005101, A153501, A005820.
%K nonn
%O 1,1
%A _Vladimir Shevelev_, Nov 01 2010
%E a(10)-a(11) corrected by _Vladimir Shevelev_, Nov 03 2010
%E Entries checked, definition shortened by _R. J. Mathar_, Nov 17 2010
%E More terms from _Michel Marcus_, Feb 06 2016