Yesterday, the best answer is: (x+1)^2e^(4x)floor(x).  (Contributed by dnialh. Good Job!)
fire solved the puzzle at 20:53:00.771; length: 2
jabrams solved the puzzle at 23:18:42.246; length: 2
Gilwall solved the puzzle at 23:20:02.657; length: 2
dnialh solved the puzzle at 23:20:20.617; length: 2
dnialh solved the puzzle at 23:20:53.703; length: 2