Annual appeal: Please make a donation to keep the OEIS running!
Over 6000 articles have referenced us, often saying "we discovered this result with the help of the OEIS".
Harland proves the conjecture of Martin & Pomerance that a(n) = n exp ((1 + o(1))(log log n)^2 log log log n) for almost all n, as well as a generalization to k-th iterates. - Charles R Greathouse IV, Dec 21 2011