sentences:  The difficulty depends on both the size and form of the number and its prime factors; it is currently very difficult to factorize large semiprimes (and, indeed, most numbers which have no small factors).The first enormous distributed factorisation was RSA-129, a challenge number described in the Scientific American article of 1977 which first popularised the RSA cryptosystem.It was factorised between September 1993 and April 1994, using MPQS, with relations contributed by about 600 people through the internet, and the final stages of the calculation performed on a MasPar supercomputer at Bell Labs.