[estptnrr] Predecessor factorization of a composite

If unable to factor a composite number N, try factoring N-1.  Is this result at all useful for factoring N?  What about the recursive prime predecessor factorization of N-1?

Probably not useful for Fermat numbers. Though it does show SNFS is possible.

Consider modifying RPPFN so that any number in the tree, not just primes, may optionally be recursively attacked with a factorization of N-1.  One possible goal is to make it smooth, avoiding large prime factors in any internal nodes of the tree.  Then some sort of SNFS?

And N+1.