RSA Labs FAQ -- Q51: What is RSA-129?

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### 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).