(you can google it for a link to a supplier)
Well worth the read. Tells the whole story of the famous "Fermat's last Theorum" problem and is extremely well written.
Fermat's Little Theorem: For any integer a and prime p, a^p is congruent to a mod p.
Fermat's Last Theorem: For any integer n > 2, there are no integers a, b, and c such that a^n + b^n = c^n.
The Little Theorem has been known for hundreds of years and is easy to prove. The Last Theorem, on the other hand, was only finally proven in 1994 by Andrew Wiles after countless failed attempts by mathematicians before him.
There is also an excellent long interview with Ken Ribet, who proved a result that inspired Wiles to take on the proof: https://www.youtube.com/watch?v=nUN4NDVIfVI