The remarkable 1,000+ bit factorization of the large composite cofactor of 21031-1 gives the factors as p74 * p225. It was reported on the NFS Discussion board on Aug 9, 2011.
Here is the text:
The composite cofactor of 2,1031- was the product of 74-digit and 225-digit prime numbers:
74-digit prime factor: 85884311010746784399233543419755720548350735429670484635313607293408440231
225-digit prime factor: 2608126619512734023079871401658597171708499248629287812371858820458873848148365066692974001408079\ 0094023694008624928430905568835328503742450614946289860645017638349124175799945515756962732171253\ 365651516226751
This is the project's first kilobit SNFS factorization. The factors will be reported to the Cunningham project and will be recorded on Page 122.
Unfortunately, this is not correct. The large number above has only 209 digits.
The 225-digit prime should be:
N = 2982096305018115260812661951273402307987140165859717170849924862928781237185
A Copy & Paste slip, no doubt.
[ The Forum entry has now been corrected by the author, after a quick email ]