High Quality Content by WIKIPEDIA articles! In mathematics, the RSA numbers are a set of large semiprimes (numbers with exactly two prime factors) that are part of the RSA Factoring Challenge. The challenge was to find the prime factors but it was declared inactive in 2007. It was created by RSA Laboratories in 1991 to encourage research into computational number theory and the practical difficulty of factoring large integers. RSA Laboratories published a number of semiprimes with 100 to 617 decimal digits. Cash prizes of varying size were offered for factorization of some of them. The smallest RSA number was factored in a few days. Most of the numbers have still not been factored and many of them are expected to remain unfactored for quite some time. As of March 2008[update], 12 of the 54 listed numbers have been factored: The 9 smallest from RSA-100 to RSA-160, plus RSA-576, RSA-640 and RSA-200.