I’ve known about Project Euler for a while, but I made the mistake of trying to use it as a vehicle to learn F#. Last week I started solving the problems with Haskell, which is vastly more fun. I highly recommend this method of recreation.
Also, this is officially the best-ever method of Fibonacci-number computation: fibs = 0 : 1 : (zipWith (\a b -> a + b) fibs $ tail fibs)