I think this is the shortest paper (1 page) with the most large title in combinatorics (24 words!):
"Alexander Burstein's Lovely Combinatorial Proof of John Noonan's Beautiful Formula that the number of $n$-permutations that contain the Pattern $321$ Exactly Once Equals $(3/n)(2n)!/((n-3)!(n+3)!)$"
by Doron Zeilberger, http://arxiv.org/pdf/1110.4379 .