Project Euler Problem 8 finding the highest product

Problem 8 of Project Euler can be done by just using a simple for loop. The problem is detailed as:

Find the greatest product of five consecutive digits in the 1000-digit number.


In C# this is pretty trivial as all we need to do is loop round mulitplying 5 digits in a row and checking if that number is higher than anything we’ve got so far. Of course you could do something elaborate with the 0s, ie not bother to calculate the product of any 5 digits containing one or more zero as it’ll always be 0. But on a modern computer this computes so fast you dont really need to code that into your answer.

Project Euler Problem 7 finding the 10001st prime

As previously mentioned in my post before I’m not going to post the complete source code for my solutions (written in C#). Instead I’m just going to talk through some of the techniques that I’ve used to solve the problems.

Here is problem 7:
By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.

What is the 10001st prime number?

Now this is actually quite easy (and quick) to solve if you know a little trick with primes. As you probably know a number is said to be prime if it’s divisible by itself and 1. A quick way of checking to see if it’s prime is to ensure that it’s not divisble by any prime lower than the square root of the number that you are checking.

Obviously as you find a new prime number you need to add it to your running list of primes so that can be used to check subsequent numbers. Using this technique gives you the answer very fast.

Project Euler


Upon reading Eric Lippert’s wonderful blog which can be found here. I read about him solving problems on project Euler for fun.

Being interesting in problem solving I decided to look up project Euler and discovered the website The website is really addictive if you enjoy solving logic problems.

I dont want to put all of the answers to the problems on here (I dont actually have them all yet) but then I figure someone could Google them and cheat. Instead I’m going to do some posts on some techniques I’ve used to solve them.