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**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

Oh no! The evil number blocks are attacking! Luckily, you happen to have a nifty prime-gun, so you can destroy those nasty numbers by shooting their own prime factors at them.

...OK, bad plot. But fun game, and surprisingly addictive.

Link here.

My best score is 3x101.

Edit: 2x2x3x37

Why did the vector cross the road?

It wanted to be normal.

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**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

I recommend having "1" be the first prime, "2" be the second prime, and so on. Not only will it take some practice getting used to (which I personally consider being a good thing for a game), but you'll also probably get a good sense of what the 5th prime is, for example, which I certainly can't name without going through the first 4 primes.

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**MathsIsFun****Administrator**- Registered: 2005-01-21
- Posts: 7,663

Great idea ... but gameplay needs improving. Needs to be "graded" (start with easy ones and build up). And manipulating left-right and then pressing the correct number key feels clumsy (to me).

"The physicists defer only to mathematicians, and the mathematicians defer only to God ..." - Leon M. Lederman

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**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

In case anyone's thinking otherwise, I didn't make this game, I just found it.

The game does get harder as you progress though. The blocks fall more frequently as the score goes up, but the score also pushes up the upper bound of the range. The blocks can take any value between 2 and the median of 100, 500 and [score+50].

I agree that having to move around rather than purely entering primes does make the game a bit clumsy, but not that much. And the only alternative I can think of would be that pressing a key will auto-target an appropriate block, which would mean you could win by just pressing them quickly without thought.

Why did the vector cross the road?

It wanted to be normal.

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**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

Edited to add: 1453 is not a randomly picked number. Why?

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**mikau****Member**- Registered: 2005-08-22
- Posts: 1,504

well its prime, and being a large number it would probably take a while for him to realize, but thats all i can observe. Is there more to it?

A logarithm is just a misspelled algorithm.

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**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

Nope, that's exactly it. The "more prime" a number is (i.e. less number of factors), the harder it is to factor. You'd have to try divisibility tests for all primes up to 37, not an easy task in a minute.

"In the real world, this would be a problem. But in mathematics, we can just define a place where this problem doesn't exist. So we'll go ahead and do that now..."

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**mikau****Member**- Registered: 2005-08-22
- Posts: 1,504

hehehe! xkcd rocks.

But hey, why would the first 37 primes suffice? (I've never really studied primes)

A logarithm is just a misspelled algorithm.

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**Ricky****Moderator**- Registered: 2005-12-04
- Posts: 3,791

Let z = x * y, with both x > sqrt(z) and y > sqrt(z). Then z = sqrt(z) * sqrt(z) < x * y = z (In other words, z < z). Contradiction, so if z = x * y, then x <= sqrt(z) or y <= sqrt(z).

It is a direct corollary that if a number is not prime, it will have a prime factor less than or equal to the square root of that number.

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**mikau****Member**- Registered: 2005-08-22
- Posts: 1,504

...cool!

A logarithm is just a misspelled algorithm.

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