Prime Bounty by Conjecture
The largest recorded known-prime number, discovered 25 Jan, 2013, is 257,885,161 − 1 (approaching 17.5 million digits). In order to illustrate the magnitude and historical importance of this discovery, a bounty of up to 2 LTC bounty can be claimed by the first post of a number-pairing (with proof) that meets the criteria of Goldbach's Conjecture for the number 257,885,161. The 2 LTC bounty decays by 3% for each day that passes with no correct answer (iow, it's, at most, a month-long contest).
Proof is required since there could be more than one answer (assuming there is one).