RSA-200 Factored

RSA numbers are composite numbers having exactly two prime factors
While composite numbers are defined as numbers that can be written as
a product of smaller numbers known as factors (for example, 10 = 2 x 5
is composite with factors 2 and 5), prime numbers have no such
decomposition (for example, 9 does not have any factors other than 1 and
itself). Prime factors therefore represent a fundamental (and unique)
decomposition of a given positive integer. RSA numbers are special types
of composite numbers particularly chosen to be difficult to factor, and they
are identified by the number of digits they contain. For knowing more about
RSA numbers and challenge problems of factorization for different-length
RSA numbers, visit the site of RSA Laboratory .

On May 9, a team at the German Federal Agency for Information
Technology Security (BIS) announced the factorization of the 200-digit
number:
2799783391 1221327870 8294676387 2260162107 0446786955 428537
5600 0992932612 8400107609 3456710529 5536085606 1822351910
9513657886 3710595448 2006576775 0985805576 1357909873 495014
4178 8631789462 9518723786 9221823983

Factorization of RSA numbers is significant because of the curious property
that proving or disproving a number to be prime seems to be much easier
than actually identifying the factors of a number. Thus, while it is trivial to
multiply two large numbers x and y together, it can be extremely difficult
to determine the factors if only their product xy is given. With some
ingenuity, this property can be used to create practical and efficient
encryption systems for electronic data.
[Main source for this posting: Mathworld.wolfram.com]