one time somebody asked me to write a code which will solve Fibonacci numbers. and I looked at the paper and after 5 secs. I told him to look at the Google this is the oldest question in the book.
I know there are some people who thinks programmer has to know this. I am not one of them actually I always like to write new things. who care the solution of Fibonacci in real world computer problems. I know what it is and how to solve it thats enough for me.
if you like to memorize that code or one of the fan of Fibonacci check this out:
http://www.hanselman.com/blog/TheWeeklySourceCode13FibonacciEdition.aspx
still I find c# 2 implementation better than others.