Yesterday, the best answer is: - 2^ (x-tan(x-1)).  (Contributed by gmode. Good Job!)
Gilwall solved the puzzle at 21:56:14.365; length: 26
fire solved the puzzle at 22:36:04.290; length: 21
dnialh solved the puzzle at 04:37:27.528; length: 16
dnialh solved the puzzle at 04:38:10.135; length: 18
Tlatoani solved the puzzle at 07:31:21.409; length: 21
blu solved the puzzle at 09:01:16.707; length: 21
1.4142135 solved the puzzle at 16:34:01.092; length: 21
person solved the puzzle at 17:22:39.359; length: 23
person solved the puzzle at 17:22:44.134; length: 23