Problem 037
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Re: problem 37 : on truncatable primes [1373 lefttruncatable?]
1 is not a prime.
Problem 37a
According to the definition of Problem 37, there exist 26 numbers that are prime truncatable (just counting the ones under 10,000,000) from both directions, not 11 as stated in the problem. I have double checked each number and all fit the description. They are (### deleted  ed_r ###). These are the ones under 10,000,000. Is the problem worded incorrectly or did I miss something? Thanks.
Re: Problem 37 Error
Please don't post answers (or attempted answers). I edited your post to remove the spoiler.
11 was one of the ones in your list. I'll leave you to work out why that's wrong ...
11 was one of the ones in your list. I'll leave you to work out why that's wrong ...
!647 = &8FDF4C
Re: Problem 37 Error
Sorry about posting possible answer.
I guess I had to check my prime number definition again. Always thought 1 was prime.
Thanks.
I guess I had to check my prime number definition again. Always thought 1 was prime.
Thanks.

 Posts: 2
 Joined: Wed Jun 24, 2009 9:17 pm
Re: Problem 037
I've found 11 such primes so far (all are under 10000) that satisfy the conditions. Before you ask, I didn't make the mistake of considering 1prime. The sum of these numbers is returned as incorrect, but I've checked and rechecked them and they all meet the requirements.

 Posts: 2
 Joined: Wed Jun 24, 2009 9:17 pm
Re: Problem 037
never mind, found my mistake.

 Posts: 2
 Joined: Fri Aug 14, 2009 10:56 pm
Re: Problem 037
Having some trouble understanding where I'm going wrong on this one. If anyone can give me a hint, PM me and I'll explain what I've done so far.
 daniel.is.fischer
 Posts: 2400
 Joined: Sun Sep 02, 2007 11:15 pm
 Location: Bremen, Germany
Re: Problem 037
First of all, if you've been told otherwise before: 1 is not a prime.
If that is not where you went wrong, PM me.
If that is not where you went wrong, PM me.
Il faut respecter la montagne  c'est pourquoi les gypaètes sont là.

 Posts: 2
 Joined: Fri Aug 14, 2009 10:56 pm
Re: Problem 037
Thanks to elendiastarman for the help. I figured out my problem, and no I wasn't counting 1 as a prime.
Re: Problem 037
I am confused  aren't five of the primes given to you in the question?!
i.e 3797, 797, 97, 379 and 37
i.e 3797, 797, 97, 379 and 37
 elendiastarman
 Posts: 410
 Joined: Sat Dec 22, 2007 8:15 pm
Re: Problem 037
You still have to find the other 6...
Want some
3.14159265358979323846264338327950288419716939937510
58209749445923078164062862089986280348253421170679...?
3.14159265358979323846264338327950288419716939937510
58209749445923078164062862089986280348253421170679...?
Re: Problem 037
Whoops, I almost crashed windows
My algoritm (written in c) searched the first 100M numbers in under 4 seconds So I thought "Oh, I can do the first 1G too". But then my prime sieve started trying to allocate 4 gigabytes of memory and that didn't work. First time memory has been a limit so far!
Not that it matters. I have more tricks up my sleeve, and found the right answer
My algoritm (written in c) searched the first 100M numbers in under 4 seconds So I thought "Oh, I can do the first 1G too". But then my prime sieve started trying to allocate 4 gigabytes of memory and that didn't work. First time memory has been a limit so far!
Not that it matters. I have more tricks up my sleeve, and found the right answer

 Posts: 1
 Joined: Sat Jan 09, 2010 3:54 pm
Re: Problem 037
Dear god, really? There are combinatoric strategies which will easily give you blinkofeye performance, there is absolutely no need for an upper bound. In fact a lot of the problems in the 3040 range have very nice combinatoric solutions  especially 34.
Also, developing and maintaining a separate prime generator/checker component that you can link in really pays off.
Anyway, I've really liked the 3040 range, I've written some of my best answers of the whole project here. My answers are meeting my collectiveblinkofeye executiontime goals well, and I'm really proud of the arbitraryradix solutions I've cooked up for most of the radixdependent problems.
I'm going to have to dig up/start the Problem 040 thread, though. My answer is a comprehensive arbitraryradix beast that takes an arbitrary array of digit indices and appears to be bugfree (it gave the right answer), but the algorithm is borderline black magic.
EDIT: Also, lol at the amount of times "1 is not a prime number" have been repeated here.
Also, developing and maintaining a separate prime generator/checker component that you can link in really pays off.
Anyway, I've really liked the 3040 range, I've written some of my best answers of the whole project here. My answers are meeting my collectiveblinkofeye executiontime goals well, and I'm really proud of the arbitraryradix solutions I've cooked up for most of the radixdependent problems.
I'm going to have to dig up/start the Problem 040 thread, though. My answer is a comprehensive arbitraryradix beast that takes an arbitrary array of digit indices and appears to be bugfree (it gave the right answer), but the algorithm is borderline black magic.
EDIT: Also, lol at the amount of times "1 is not a prime number" have been repeated here.
Re: Problem 037
I know. I had long ago solved the problem, and was just fooling around seeing if I could make the code faster, and seeing how its timing behaved with higher upper bounds. It's always fun to perfect code once you've solved a problem.Fenrisulvur wrote:Dear god, really? There are combinatoric strategies which will easily give you blinkofeye performance, there is absolutely no need for an upper bound. In fact a lot of the problems in the 3040 range have very nice combinatoric solutions  especially 34.
I just thought it was funny that my memory actually gives the upper bound on how many primes I can generate. Though I could always use bits. Still that's only an order of magnitude.
But I'm pretty proud that my code is that fast.
Problem 037
In Problem 37 you are supposed to find 11 primes. My program finds 10 primes pretty quickly, but then takes forever and bumps into the limit I have set up.
My method is a pretty brute force algorithm.
The question I have is: Is the 11th number considerably bigger than the 10th number, or is my program simply wrong in some way?
My method is a pretty brute force algorithm.
The question I have is: Is the 11th number considerably bigger than the 10th number, or is my program simply wrong in some way?
Re: Problem 037
Please don't start a new topic for a problem when there already exists one.
Re: Problem 037
Yes, the 11th and final number is quite a bit larger than the 10th. Raise your limit.Osprey wrote:In Problem 37
The question I have is: Is the 11th number considerably bigger than the 10th number, or is my program simply wrong in some way?
You could also try to figure out a more clever algorithm. My Java program finishes in less than a second, and it does not have a limit of 11 solutions or any maximum number. It knows when to give up.
Re: Problem 037
Thanks you for the assertion, I'll try to make my program a little intelligent

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 Joined: Mon Aug 15, 2011 4:38 pm
Re: Problem 037
Just how bigger the eleventh number is?
It takes 7 seconds for my algorithm to produce 10 numbers, but the 11th is still way too far away. Approximately how faster should my algorithm be?
It takes 7 seconds for my algorithm to produce 10 numbers, but the 11th is still way too far away. Approximately how faster should my algorithm be?