BEWITCHED NUMBER: "I need a mathematician to be my assistant", - says the instructor, - "his/her task is very simple: I shall enumerate different numbers. My assistant's task is to name the numbers more by one than the numbers I name. c.f. If I say "eight", the assistant must say "nine". If I say "thirty - two" the assistant must say "thirty three" etc. Who can "cope with this task?" The instructor names the increasing numbers. The numbers increase by tens and hundreds. Every time the assistant confidently names the numbers more by one. The counting continues until the instructor names number "4099". At this number the assistant will make a mistake. Instead of "4100" he/she will say "5000".