 In a letter to Euler written in 1742, Christian Goldbach conjectured that all even numbers greater than 2 are expressible as the sum of two  primes.[7]  Over the following two and a half centuries, mathematicians have been unable to prove Goldbach’s Conjecture. However it has been verified for many billions of examples, and there appears to be a consensus among mathematicians that the conjecture is most likely true. Below is a partial list (as of October 2007) showing the order of magnitude up to which all even numbers have been checked and shown to conform to GC.