This question already has an answer here:
If someone with not much mathematics in his luggage asks me: What is so special about $\pi$? then off course I have an answer. Even if $i$ would be the subject (I allready see him gazing at my mysterious smile). But when I am asked about $e$ then I grow silent (or try to change the subject). Please help me out of this. Give me a nice characterization of $e$.
I am informed now that this question is somehow a duplicate of this. I agree with that judgment. Sorry for that. Next time I will first have a closer look at the questions that have allready been asked. Thank you also. I find very nice answers there and advice everyone interested to have a look.