Find the sum of the multiples of 13 or 3 under 535

Too hard? Here's a detailed example:

Find the sum of the multiples of 3 or 5 under 16

Walk through each number from 0 to 15

For each number, check if it is a multiple 3 or 5 or both.

If it is, take note of that number. If it is not, ignore it.

At the end of this process, you should get: 3, 5, 6, 9, 10, 12, 15

The sum of those numbers is: 3+5+6+9+10+12+15 = 60

The solution is therefore 60.

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