Try Project Euler:
Project Euler is a series of
challenging mathematical/computer
programming problems that will require
more than just mathematical insights
to solve. Although mathematics will
help you arrive at elegant and
efficient methods, the use of a
computer and programming skills will
be required to solve most problems.
The problem is:
Add all the natural numbers below 1000
that are multiples of 3 or 5.
This question will probably introduce you to Python for-loops and the range() builtin function in the least. It might lead you to discover list comprehensions, or generator expressions and the sum() builtin function.
