RSA-260 Factored: 35-Year Challenge Falls

Episode 1 · Claimed Factor of RSA-260 Sparks Speculation of AI Involvement (2026-09-03, 3 posts)

X user @penlume posted a claimed factor of RSA-260, an unfactored RSA challenge number, sparking widespread astonishment and speculation about possible AI involvement. If verified, it would be a landmark result in integer factorization.

• Unverified claim: 200-digit number posted that supposedly divides RSA-260 — marvinvonhagen · 2026-09-03
• A huge 176-digit integer is claimed to divide RSA-260, unverified — CatAstro_Piyush · 2026-09-03
• Claim: a 129-digit number divides RSA-260, shocking the AI crowd — rickasaurus · 2026-09-04

Episode 2 · RSA-260 Challenge Number Factored After 35 Years, Setting New Record (2026-09-03, 6 posts)

Cognition engineer Eric Lu (@penlume) announced on X that he had factored RSA-260, a 260-decimal-digit (about 862-bit) RSA Factoring Challenge number that had stood unbroken for 35 years, setting a new world record for general-purpose integer factoring. He announced the result with a single sentence and posted two 130-digit factors, both passing primality checks. The event matters both as a long-standing cryptographic milestone falling and as a showcase of X as a live gathering place for the cryptography community.

Confirmed

• Eric Lu published two 130-digit factors of RSA-260, both passing primality tests, completing the factorization of the 260-digit (862-bit) challenge number.
• According to @MikePFrank, the factorization took about 7 months.
• The previous record was the 2020 factorization of RSA-250 by an academic team using CADO-NFS; per cryptographer Steve Weis (relayed by @matthewdgreen), it consumed roughly 2,700 core-hours of computation.
• Within two hours of the tweet, a member of the team that factored RSA-155 in 1999 appeared in the replies to congratulate him—an achievement completed "before @penlume was born."
• Per @marvinvonhagen, the relevant Wikipedia entry was updated only minutes after the tweet.

Why it matters

• RSA-260 was an iconic, long-unsolved number in RSA Laboratories' factoring challenge; its factorization directly refreshes the world record for general-purpose integer factoring.
• The congratulation from the 1999 RSA-155 veteran added a community-legacy note that multiple relays (@marvinvonhagen, @k7agar) highlighted.

• RSA-260 Factored, Setting a New World Record for General-Purpose Number Factorization — marvinvonhagen · 2026-09-03
• RSA-260 factor posted, RSA-155 legend shows up in replies within 2 hours — k7agar · 2026-09-03
• RSA-260 factored after 35 years: Cognition engineer Eric Lu did it by hand in 7 months — MikePFrank · 2026-09-03
• RSA-260 Factor Tweet Draws Congrats From 1999 RSA-155 Team Within 2 Hours — marvinvonhagen · 2026-09-04
• New RSA-260 Factoring Record Set, Following RSA-250's 2,700 Core-Hour Effort in 2020 — matthew_d_green · 2026-09-04
• RSA-260 factored: decades-old 862-bit cryptology challenge finally falls — Daniel_Lerch · 2026-09-05