which was factored by Brent & Morain in
1988. 
was factored by
A.K. Lenstra, H.W. Lenstra Jr., M.S. Manasse & J.M. Pollard
in 1990. 
was factored by Richard Brent who found a 40-digit factor
of 
on October 20, 1995. The cofactor is
a 252 digit number, which is not so easy to factor. Luckily,
this number was also prime.