# Math 380 - Lab I

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## Project Euler

For the next few weeks, we'll focus on Project Euler - like questions. A key component of these problems is that they are generally meant to be solved with a short computer program. Usually, a little mathematical insight will make the difference between a program that runs in a reasonable amount of time and one that does not. To get the basic idea, let's take a look at the first problem:

#### Project Euler question 1

If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.

Find the sum of all the multiples of 3 or 5 below 1000.

While quite easy, this problem illustrates the general idea. Typically, there's an easier version of the problem that allows you to check your work; I call this the pre-problem. Then, the question itself requires either more computing power or a more clever algorithm.

Let's take a look at some Python code that solves the pre-problem.

Note that's live code. Hit the "Evaluate" button to generate the answer. Do you see how to modify the code to get the answer to the actual question?

## Improving our code

Let's suppose now that we'd like to find the sum of all numbers less than 1 million that are divisible by 17 or 19. Emulating the code above (and including some code to time the computation), we might write:

That is not particularly fast. Rather than checking every, though, we can simply list every seventeenth and nineteenth number starting from zero. I guess we'll have to remove the ones that we counted twice, though. Here's some code that uses that approach:

Well, that's a lot faster!

### Problem 1

Find the sum of all the multiples of below .

To submit your solution, you should respond to my email with subject line "Problems Lab 1 #1". Be sure to include the Sage Cell Server's Short link to the Python code that you wrote to generate your solution.