# Tagged Questions

Project Euler is a series of challenging mathematical/computer programming problems. Please see the site and rules before posting.

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### Need to find a better algorithm to solve a project euler problem dealing with coprime pairs.

I've been working on this for a while and found several solutions so far, but none are fast enough to find the necessary $S(10^7)$. Here is the question: For an integer $M$, we define $R(M)$ as ...
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### Primality and repeated digits

I recently worked on problem 51 through project euler, I solved it essentially through brute-force but afterwards I viewed the forum and there were some more clever solutions. For those unfamiliar ...
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### Steps to get Inverse of Pentagonal

I have solved http://projecteuler.net/problem=44 by getting the inverse equation from Wikipedia http://en.wikipedia.org/wiki/Pentagonal_number: Pentagonal: $f(n) = \frac{n(3n - 1)}{2}$ Inverse ...
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### How to find large prime factors without using computer?

What is the largest prime factor of the number 600851475143 ? This is the third problem of Project Euler. How to approach this mathematically (without computer programming) ?
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### sum of even-valued and odd-valued Fibonacci numbers

I was solving the Project Euler problem 2 *By starting with 1 and 2, the first 10 terms of Fibonacci Series will be: 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ... Find the sum of all the even-valued terms ...
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### Euler's Numerical method help

Consider this differential equation, $dy/dx = x + \sin(y)$ with initial condition $y = 0.5$ when $x = 1.2$: Write down the recurrence relation for Euler's numerical method applied ...
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### Finding all possible paths from one corner to the other on a grid, without backtracking

Me again "new to maths guy". Please tell me if the substance of my questions are not a good fit for the site. I'm now onto Question 15 of Project Euler and it seems like there's some mathematical ...