Euler Problems: Code or Computing Power?

Hey all,
I love the Euler Problems for short coding exercises, but often I am stuck because I cannot find the solution. Coding the basic function is often easy, but then the code should be applied to really large numbers and I dont see how this will work out. Take this example here: https://projecteuler.net/problem=501
The Code is not long, but even plugging in 10^5 takes my PC like 5 mins to solve. How am I supposed to do this with 10^12??? I mean, is my code just bad and wasting 90% of the time or what is the "trick" to these ones?