Author 
Message 
rmplpmpl
Joined: 26 Oct 2008 Posts: 113 Location: Germany 

Big Fib 

Ok, another problem I have  I want to believe I got the correct number and the answer but it is not accepted.
Anyway, could please someone tell me if the number I have is correct, starting with 11742003035506558... and ending with ...32895630172796932853738956168354898000000
the six zeros at the end tell me that I might have a glitch in my computation...


Sun Nov 02, 2008 1:01 am 


MerickOWA
Joined: 07 Apr 2008 Posts: 182


Re: Big Fib 



Ok, another problem I have  I want to believe I got the correct number and the answer but it is not accepted.
Anyway, could please someone tell me if the number I have is correct, starting with 11742003035506558... and ending with ...32895630172796932853738956168354898000000
the six zeros at the end tell me that I might have a glitch in my computation... 
Can't be a prime and end in zeros It would trivially be divisible by 2 or 5


Sun Nov 02, 2008 2:05 am 


the_impaler
Joined: 30 Apr 2008 Posts: 61


Re: Big Fib 

[quote="MerickOWA"]
Can't be a prime and end in zeros ;) It would trivially be divisible by 2 or 5 ;)[/quote]
How do you know that it "can't be a prime" ? 13 is prime and so is 233 and there are more.
Of course you know because you have found it but off the bat it's hard to say.
That would probably give adum another crazy number crunching idea like "find the prime fib that has last 100 digits matching pi in reverse"


Sun Nov 02, 2008 2:28 am 


sigi
Joined: 26 Oct 2008 Posts: 37




I have no idea what Merick is talking about... anyway: you're supposed to give every 20,000th digit of the 1.5 millionth Fibonacci number  and your answer is having a string of zeroes at the end. I would like to say that it's extremely unlikely that you answer is correct.
I'm not a number theorist but I'm guessing that the answer to this challenge pretty much amounts to a random number  meaning that every digit is roughly equally likely.
There's not that much that can go wrong with this challenge (or the coding involved). Just recheck your code.


Sun Nov 02, 2008 6:50 am 


rmplpmpl
Joined: 26 Oct 2008 Posts: 113 Location: Germany 





I have no idea what Merick is talking about... anyway: you're supposed to give every 20,000th digit of the 1.5 millionth Fibonacci number  and your answer is having a string of zeroes at the end. I would like to say that it's extremely unlikely that you answer is correct.
I'm not a number theorist but I'm guessing that the answer to this challenge pretty much amounts to a random number  meaning that every digit is roughly equally likely.
There's not that much that can go wrong with this challenge (or the coding involved). Just recheck your code. 
Yupp, I know that 20,000th digit part and I could extract THAT part easily, but since I obviously got the wrong number, the resulting digits were wrong, too. Bah, back to computation.
Thumbs up to these challenges who make me learning stuff!


Sun Nov 02, 2008 10:53 am 


gfoot
Joined: 05 Sep 2007 Posts: 269 Location: Brighton, UK 



I just recalculated it  I get the same ending as you, but a different beginning. Maybe you calculated the 1499999th instead.


Sun Nov 02, 2008 11:34 am 


MerickOWA
Joined: 07 Apr 2008 Posts: 182


Re: Big Fib 



How do you know that it "can't be a prime" ? 13 is prime and so is 233 and there are more.
Of course you know because you have found it but off the bat it's hard to say.
That would probably give adum another crazy number crunching idea like "find the prime fib that has last 100 digits matching pi in reverse" 
It can't be prime if the last digit is a zero. Any number that ends in zero is divisible by 10, and thus NOT prime.
Same way I can trivially prove that every prime (except 2 and 5) must end with either 1, 3, 7 or 9. If it ended in 0,2,4,6,8 it would be even and thus divisible by 2. If it ends in 0 or 5 its divisible by 5.


Mon Nov 03, 2008 5:58 am 


MerickOWA
Joined: 07 Apr 2008 Posts: 182




Ok ignore me, I was thinking of a different problem were you have to calculate a big prime number fibonacci numbers are different sorry


Mon Nov 03, 2008 6:02 am 


eike42
Joined: 26 Oct 2008 Posts: 15




I have the same value... either its correct, or we're using the same codebase:
Used this one: http://www.bigzaphod.org/fibonacci/
My own perl script was too damn slow and I was to lazy to write C code


Mon Nov 03, 2008 8:23 am 


rmplpmpl
Joined: 26 Oct 2008 Posts: 113 Location: Germany 





I have the same value... either its correct, or we're using the same codebase:
Used this one: http://www.bigzaphod.org/fibonacci/
My own perl script was too damn slow and I was to lazy to write C code 
hm, I used another tool (Formula One IDE) for computation of the number and a generic tool to extract the digits asked for. Length of "my" number is 67170, so the solution had four digits.


Mon Nov 03, 2008 10:43 am 


snibril
Joined: 26 Oct 2008 Posts: 31




fib(1500000) can be computed in under 5min on a Phenom 9850 with bc under linux and has more than 300000 digits.


Mon Nov 03, 2008 12:14 pm 


hoki
Joined: 28 Oct 2008 Posts: 5




I'm kinda stuck here. First I computed what I thought was the right number using bc. Then I noticed it asked for the 1,500,000th member of the Fibonacci sequence instead of fib(1.5m), so I recalculated. Still my solutions don't seem to be correct.
My number starts with "19768781" and ends with "345698". It has 313481 digits.
Did I get it right that you want the first digit, then take a 20,000step, that digit (20001th) and so on? Or do you want the first and the k*20,0000th digits, with k = 1,2,...
Bye,
hoki


Wed Nov 05, 2008 2:51 pm 


snibril
Joined: 26 Oct 2008 Posts: 31




It starts with 129... and ends with ...000


Wed Nov 05, 2008 3:00 pm 


brazzy
Joined: 07 Nov 2008 Posts: 14 Location: Munich, Germany 



I think one reason why many people are having problems is that some definitions of the Fibonacci sequence have it start with 0 and 1, and others start with 1 and 1, so that the numbering is one off between those two definitions.


Thu Dec 04, 2008 6:29 pm 


abc
Joined: 02 Nov 2008 Posts: 12


Fib 1 = 1 

Hi!
I think everybody should know that the first fib=1 in this challenge. (not 0)
Still got the same problems...
abc


Fri Dec 05, 2008 7:57 pm 


