There is no solution to the equation "a*n + b*n = c*n"
(where '*' is 'to the power of', a, b, and c are whole numbers greater than 1, and 'n' is greater than 2).
Fermat's Last Theorem
by Simon Singh
Simon researched Andrew Wiles' road to mathematical fame for a television programme, but the book accompanying the programme proved even more popular. Written in an engaging style as a detective story, you can't help but be drawn into the excitement that surrounded the possibility of a proof worked on in secret for seven years.
Also, for enthusiasts, here's a blog dedicated to explaining the theorem and Andrew Wiles proof:
The blog has been going for four years now, so it gives you an idea of how complex the proof is.
Luckily, it won't take you that long to read the book!