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 Post subject: Brainteaser thread
PostPosted: Sun May 04, 2008 9:53 pm 
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This is a tradition in many forums I frequented in the past. With an intelligent base of participants it can prove to be a lot of fun. :joker:

The rule is quite simple. Each time a brainteaser is posted, and others race to figure out the correct answer. The winner gets the right to post the next brainteaser. If he/she doesn't want to post one he/she can concede the right to another poster appointed by him/her, or forfeit it to the general public. In the latter case everyone can post the next brainteaser. If 2 or 3 posters post in quick succession, the fastest one's brainteaser becomes the current one and the others' brainteasers are put into the waiting list. The next winner can then either post his/her own brainteaser or pick one from the waiting list.

But the poster of the current brainteaser need to keep track of this thread frequently and promptly address the correct answerer, so as not to stall the thread unnecessarily. If a brainteaser gets unanswered for 5 days it is automatically put into the waiting list and the next brainteaser can be posted by anyone. The current poster can avoid this by gradually providing extra hints to his/her brainteaser.

And another important rule is: if one uses online tools such as Google, Wikipedia, Yahoo Answers to find the answer, one is not allowed to post the answer unless the brainteaser is unsolved for 3 days or more. This is to prevent unsportsmen spoiling the fun for others cheaply. Of course it's all self-monitoring but most participants I played with in the past are quite honest. :thumbs:

So enough of the laws. Let's play! :viking: I'll start the 1st one:

Brainteaser #1:

Why is 6842075193 a special number?

Note I also posted this in the sudoku.com & djape.net forums. But for some reasons I bet people here will be the quickest to crack it. :ugeek:

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 Post subject: Re: Brainteaser thread
PostPosted: Sun May 04, 2008 11:16 pm 
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No answer yet, but it has all the digits 0-9, and all evens before the odds. Its digits sum to a multiple of 9 so it's definitely not prime.
Its factorization is 3^2*2663*9209. A useless piece of information I'm sure.

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 Post subject: Re: Brainteaser thread
PostPosted: Mon May 05, 2008 2:51 am 
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Glyn, nice effort but no luck yet. Press on! :applause:

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 Post subject: Re: Brainteaser thread
PostPosted: Mon May 05, 2008 8:20 am 
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udosuk wrote:
Why is 6842075193 a special number?
The number of people that will be watching udosuk doing :bouncy: at the Olympics?
Is it about the olympics?
Is it about population?

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 Post subject: Re: Brainteaser thread
PostPosted: Mon May 05, 2008 10:32 am 
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Not only are the digits partitioned (even then odd) but they fit the form
|e-d|,|d-c|,|c-b|,|b-a|,0,a,b,c,d,e
where || is the modulus. Another curious and probably irrelevant piece of info.

As is the that fact 75193 is prime. Unfortunately so are numerous others the lowest being 13597, the highest 95731.

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 Post subject: Re: Brainteaser thread
PostPosted: Mon May 05, 2008 12:04 pm 
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The digit differences looked interesting. From non-repeated odd digits from 1-9 we can form a set of 5 digit numbers.

Interestingly, or maybe not, the numbers:- 19375,35917,39157,53719,57391,75193,91735,91753 were the only ones where adjacent digits differed by distinct even amounts (2-8). Four were prime so that didn't help.

If we filter them again taking the difference between next nearest neighbours only 3 remain:- 35917,39157 and 75193. The last 2 are prime though I think now that that has nothing to do with the puzzle. I can't split them by further differencing. So my dead end at the moment is:-

75193 is the largest number constructed from disjoint odd digits, with disjoint differences between neighbouring digits and 'next neighbour digits'

I've already pointed out the relationship between the first 4 even digits (6842) and the the last 5 (75193), or rather their reverse (39157), but now I'm stuck again.

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 Post subject: Re: Brainteaser thread
PostPosted: Mon May 05, 2008 1:59 pm 
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It is the secret private phone number (684-207-5193) of the American president?

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 Post subject: Re: Brainteaser thread
PostPosted: Mon May 05, 2008 2:07 pm 
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Ed, I wish that many people will be watching me slam dunk against the Dream Team or bounce up and down on a trampoline in Beijing this August. :bouncy: But no. The answer is purely metagrobological, nothing to do with sports/olympics/population or any of similar facts/statistics.

Major Major Major Glyn, you truly deserve your special title. Although not finding the correct answer yet your effort has certainly impressed me a lot. Have to tell you to find my answer you need to attack from a totally different angle but nothing prevents me from regarding your reasons as very logical and reasonable themselves too. Hopefully my "model answer" will not disappoint you. :alien:

Børge wrote:
It is the secret private phone number (684-207-5193) of the American president?

Aha! Glad to see googling doesn't help you out here. It wouldn't be special at all if it can connect you to Mr. Dubya (in fact it will be very boring). Perhaps it'd be a little bit interesting if it can connect you to Osama, Obama or Chelsea's Mama! :dude: Seriously, the answer to the puzzle has no linkage to any particular human being at all... :geek:

Let me give another small hint to hopefully help you guys out a bit:

Hidden Text:
By reversing the number (3915702486), it is still special no less.

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 Post subject: Re: Brainteaser thread
PostPosted: Mon May 05, 2008 2:59 pm 
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I did wonder if it was the phone number of a certain Dutch metagrobologist.

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 Post subject: Re: Brainteaser thread
PostPosted: Tue May 06, 2008 7:40 am 
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Glyn wrote:
... but it has all the digits 0-9 ...

This bit is relevant. :idea:

I'll post a major hint tomorrow after the Cavs-Celtics NBA game. :ugeek:

I just want to add a rule that after the puzzle stays unsolved for 5 days the poster has the choice to reveal the answer or put them into the waiting list (so that others can continue to try at any time). Then anyone can post the next brainteaser. Just don't want to hog the thread with a particularly nasty question, which this one is becoming. :pallid:

In that case I'll reveal the answer on the 10th of May if nobody has managed to find the answer. In the mean time I'll keep giving out hints so hopefully it won't come to that. And then hopefully someone will provide a nicer brainteaser! :pray:

I have a fetish belief that any brainteaser which you can find the answer within a minute by googling is not a good one, but I guess some of these types could work better for this thread, the problem is then we need to rely on the conscience of players... :geek: Or maybe this thread is not that good an idea after all... :scratch:

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