$ erl
Erlang R14B02 (erts-5.8.3) [source] [smp:2:2] [rq:2] [async-threads:0] [hipe] [kernel-poll:false]
Eshell V5.8.3 (abort with ^G)
1> c(onion).
{ok,onion}
2> onion:run(5).
5
3> onion:run(10).
55
4>
-----------------------%-
onion:run(N) prints Nth Fibonacci number, but it can do much more...