### Question 51. What is RSA-129?

*RSA-129* is a 129-digit (426-bit) integer published in Martin
Gardner's column in *Scientific American* in 1977. A prize of $100
was offered to anybody able to factor the number. The number was factored
in March 1994 by Atkins *et al*.
[AGL95] using the resources of 1600
computers (which included two fax machines) from the Internet. The factoring
took about 4000 to 6000 MIPS years of computation over an eight-month period.
It was factored using the quadratic sieve factoring method and, according
to Lenstra, will perhaps be the last large number to be factored using
the quadratic sieve since the general number field sieve is now more efficient
for numbers of this size and larger (see Question 48).