Shorten an already short mathematical expression
Emotinomicon, 48 bytes / 13 characters

I do it, not because it is short, but because it is fun. Try it here. You'll have to copy+paste it into the textbox.

⏪✖➕⏩


Explanation:

  ⏪       ✖       ➕         ⏩   explanation
                                              take numeric input
    ⏪                                           open loop
                                              duplicate top of stack
                                              push pi
                ✖                               multiply top two elements on stack
                                              reverse stack
                                              pop N, push e^N
                            ➕                   add top two elements on stack
                                              take numeric input
                                              duplicate top of stack
                                              pop N, push N+1
                                            ⏩   close loop


Here is the program in its native environment, the mobile phone: