The Fermat's Last Paradox calls attention to the fact that there ought to be many deceptively simple math problems with elusive (simple?) proofs in the margins of notebooks, but only the one has come to our attention thus far.
@futurebird Well, this one became so famous partly because Fermat left a lot of marginal notes, and most of his other insights turned out to be true, just much easier to prove.
@riley@futurebird Fermat used to troll English mathematicians by writing them letters detailing theorems he had proven and not including the proof, and being like "Can you prove this? I bet not, because you are English"
@ellenor2000@riley@futurebird But the point is this was another thing that had contributed to the "well if he said he proved it, he must have really done it" thinking, because he'd publicly claimed implausible proofs that were later found proven in his personal papers