A number theorist's twin-prime reciprocal-sum project, not a chip test, publicly surfaced the Pentium FDIV bug in 1994

The Intel Pentium's floating-point division defect became public knowledge not through Intel's quality-assurance process or any deliberate test of the divide instruction, but as a side effect of pure mathematics. In June 1994 Thomas Nicely, a mathematician at Lynchburg College in Virginia, was extending a long-running computation of Brun's constant — the sum of the reciprocals of the twin primes — onto a new Pentium machine when his cross-checks against results from non-Pentium hardware began to diverge. Vaughan Pratt's 1995 post-mortem records that "the error was first noticed within Intel and independently by Prof. Thomas Nicely... in the course of an ongoing project to estimate the sum of the reciprocals of the twin primes, known to exist but not known to much accuracy."

Nicely reported the discrepancy to Intel on 24 October 1994. When Intel did not act, he circulated the finding on 30 October via Usenet and CompuServe, and it "quickly became a cause célèbre on the Internet" (Pratt 1995), forcing Intel's hand. Intel had reportedly detected the flaw internally before Nicely, but it was the outside number theorist's disclosure that made it a public event.

The discovery vector is the notable structure here: the defect lived in the divide unit, but no one was auditing division. It surfaced because someone building an unrelated tower of reciprocal sums noticed the tower did not add up. This is the concrete, in-the-wild counterpart to the abstract object at the root of claim-linnainmaa-rounding-error-problem — the sensitivity of an accumulated result to a local arithmetic error — and a sibling case to claim-patriot-dhahran-1991-clock-drift-from-24-bit-truncation-of-tenths, where a floating-point defect also revealed itself only through downstream drift. The underlying hardware fault is described in claim-pentium-fdiv-bug-five-missing-srt-lookup-table-entries; the corporate aftermath in claim-intel-475m-charge-pentium-fdiv-recall.