Largest Prime Factor of 600851475143

[Arman777]

Your refusal to write pseudocode is a mistake. Just sayin'.

I am writing and I am thinking about it. Just when I write the codes things happen.

 

[Arman777]

I found it. Not in a direct way but I find it anyways
my code

N=600851475143
b=1
while True:
    if N%b==0:
        t=N//b
        b=b+1
        print (t)
    else:
        b=b+1

 

[scottdave]

Another sad thing is this is the 3rd problem in the project euler site

Sorry you're having such a time, but thanks for sharing the website,
https://projecteuler.net

I think that's just what I need for some practice problems.
I'm on my phone and I did the 1st one on my phone using Google Sheets while my kid is at swim practice .
not everything has to be done in Python

 

[scottdave]

Your refusal to write pseudocode is a mistake. Just sayin'.

Or a flowchart, perhaps.
I used a spreadsheet to solve this. Maybe I'll go try to write some code. I'm taking an online Python right now, so I think the extra practice will be good. But often you can use other tools.

My approach was to go along till I hit a factor, check to see if that number is prime. Take the original number 600851475143 and divide by that factor. Now I have a somewhat smaller number to find factors of. The next number that turns up to be a factor, divide by that one and I have a smaller number.
If you keep track of the product of these factors you've been saving, then you will know when to stop.

 

[Arman777]

Sorry you're having such a time, but thanks for sharing the website,
https://projecteuler.net

I think that's just what I need for some practice problems.
I'm on my phone and I did the 1st one on my phone using Google Sheets while my kid is at swim practice .
[emoji2] not everything has to be done in Python

Yes and I actually come here to thank @StoneTemplePython for introducing me to the site, but I saw your post so your welcome somehow :)

I come to the 9th problem ( I solved the earlier ones as well) and I'll try to do more and more, Its really great indeed.

Or a flowchart, perhaps.
I used a spreadsheet to solve this. Maybe I'll go try to write some code. I'm taking an online Python right now, so I think the extra practice will be good. But often you can use other tools.

My approach was to go along till I hit a factor, check to see if that number is prime. Take the original number 600851475143 and divide by that factor. Now I have a somewhat smaller number to find factors of. The next number that turns up to be a factor, divide by that one and I have a smaller number.
If you keep track of the product of these factors you've been saving, then you will know when to stop.

Well, I guess that's a good approach, the interesting thing is 4th, 5th or 6th problems are much easier than the 3rd one somehow (at least for me).
7th took some time to solve but I manage to do it.
8th is really nice :) If you are doing good or want to share your code (after solving) I can also share mine.

Edit:Also I should mention that first 100 problem is catagorized as easy so I am going slowly :)

 

[StoneTemplePython]

.
I'm on my phone and I did the 1st one on my phone using Google Sheets while my kid is at swim practice .

I'm taking an online Python right now, so I think the extra practice will be good. But often you can use other tools.

Btw, if you have an iPhone and/or iPad, I'd strongly recommend getting Pythonista. You can run Python scripts with any of the standard module imports (plus numpy if you want) and it runs great on both. I don't think its available on Android, unfortunately.

A few years ago, I would spend a lot of time on iPhone or iPad coding via Pythonista while waiting for train or bus (and sometimes while riding the train too depending on crowding). Getting an extra 20 - 40 mins in every day during waiting time really adds up in terms of scaling the learning curve.
- - - -
High level: my general approach is scribble something down with pen and paper first, then straight to Python. I don't use Pythonista much these days but I have fond memories.

 

[scottdave]

I come to the 9th problem ( I solved the earlier ones as well) and I'll try to do more and more, Its really great indeed.

Well, I guess that's a good approach, the interesting thing is 4th, 5th or 6th problems are much easier than the 3rd one somehow (at least for me).
7th took some time to solve but I manage to do it.
8th is really nice :)

I haven't gone exactly in order. I'll work on one for a little while, then move on to another if I feel I'm stuck, then come back to revisit. These are the ones that I've solved so far: 1 thru 3, 5 thru 11, 13, 16, 19, 20, 22, 26, and 29

 

[Arman777]

I haven't gone exactly in order. I'll work on one for a little while, then move on to another if I feel I'm stuck, then come back to revisit. These are the ones that I've solved so far: 1 thru 3, 5 thru 11, 13, 16, 19, 20, 22, 26, and 29

Thars great :) Sure you can

 

[Fred Wright]

Some suggestions:
https://en.wikipedia.org/wiki/Quadratic_sieve
https://en.wikipedia.org/wiki/Pollard's_rho_algorithm

Peace,
Fred

 

[willem2]

Some suggestions:
https://en.wikipedia.org/wiki/Quadratic_sieve
https://en.wikipedia.org/wiki/Pollard's_rho_algorithm

I haven't seen any problem where those are necessary. I found a 450-line version of the quadratic sieve online.
Implementing that by yourself is probably harder than any projecteuler problem.
Pollards_rho_algorithm is simple enough, if you think you need it.

What is useful many problems is generating a list of primes with https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
You can easily go up to 10^7 in python in a second or so. You could also store the smallest factor of each number in the sieve. This will get you instantaneous factoring.