Fermat's Last Theorem is an algebraic statement proposed by Pierre de Fermat.
Following his death, a mathematical formula scrawled in the margin of his notes, " where is greater that 2" which Fermat said had no solution in whole numbers, but he also add a phrase, "remarkable proof".
According to Jean-Luc Picard, people have been trying to solve the proof for 800 years, including himself, during his pastime. Picard found it stimulating, and noted that it put things in perspective stating that "in our arrogance, we feel we are so advanced and yet we cannot unravel a simple knot tied by a part-time French mathematician working alone without a computer." (TNG: "The Royale")
Jadzia Dax stated that one of her previous hosts, Tobin Dax, had "the most original approach to the proof since Wiles over 300 years ago." (DS9: "Facets")
Background
"The Royale" aired in 1989, four years before a proof for Fermat's last theorem was published by Andrew Wiles. The mention in "Facets" may be understood as a subtle correction for the incongruency.
Fermat had claimed that he had found a simple proof for his last theorem without ever presenting it. No written records of that alleged proof could be found after his death. The proof by Wiles was lengthy, complex and essentially required advanced 20th century mathematical concepts, so it is extremely unlikely that Fermat had known Wiles' proof. So even if Fermat's last theorem was proved in 1993, the question remains open whether the simple proof Fermat claimed to have found exists or not.