www.mikescher.com/www/statics/euler/Euler_Problem-048_explanation.md

I like the occasionally really easy problems between the others. It's like a little break sometimes.

The "trick" here is to understand the modulo operator. If you have (a + b) % c you can also write a%c + b%c. And also you can write (a * b)%c as (a%c) * (b%c).

So all we do is calculate the sum kinda normally, but we do modulo 10^10 after each step (every addition and multiplication). We guarantee this way that out numbers never exceed the range of an 64bit integer.