Quote:
Originally Posted by axn
what is the form of factors for these numbers? It will be k*2^14+1, but will k itself has other restrictions (like k is a multiple of 2 or 4 or something? other modular restrictions?)

I would say the multiplier must be even, so it becomes (under a new convention where k is odd) \(k\cdot 2^n + 1\) where \(n \ge 15\). See also
New GFN factors (Wilfrid Keller).
/JeppeSN