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**Mathegocart****Member**- Registered: 2012-04-29
- Posts: 1,882

1. For the set of positive integers from [1, 10000], find the sum of all values of x such that x^2 + 27 and x + 3 are prime.

*Last edited by Mathegocart (2017-01-02 12:41:30)*

The integral of hope is reality.

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi;

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**Mathegocart****Member**- Registered: 2012-04-29
- Posts: 1,882

bobbym wrote:

Hi;

You did that with M, I presume?

The integral of hope is reality.

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Is there anything better?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**phrontister****Real Member**- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,592

Hi;

I got the same answer as Bobby's, also with M.

There are 236 solutions to "all values of x such that x^2 + 27 and x + 3 are prime".

*Last edited by phrontister (2017-01-13 01:35:47)*

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Very good work!

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**phrontister****Real Member**- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,592

The right tool for the job!

I tried using Table instead of For etc, but couldn't see how.

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi;

For a functional approach:

`Select[Range[10000], PrimeQ[#^2 + 27] && PrimeQ[# + 3] &] // Total`

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**phrontister****Real Member**- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,592

Yes, the functional approach is what I was trying for.

Just having a go now with your code to get it to return the x count as well. That would be via Length, I guess.

...but lunch first.

...and may have to go out soon after.

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Yes, Length is the command that will tell you how long that list is. You can try this.

```
Select[Range[10000], PrimeQ[#^2 + 27] && PrimeQ[# + 3] &];
Total[%]
Length[%%]
```

Have a good lunch.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**phrontister****Real Member**- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,592

Very yummy lunch, thanks, followed late afternoon by even yummier birthday party food!

That's a neat trick, using %n to choose specific output lines! It does away with introducing another variable, unlike the following variations of your code...

Mine:

```
p=Select[Range[10000],PrimeQ[#^2+27]&&PrimeQ[#+3]&];
Total[p]
Length[p]
```

SE1:

`p=Select[Range[10000],PrimeQ[#^2+27]&&PrimeQ[#+3]&];#[p]&/@{Total,Length}`

SE2:

`p=Select[Range[10000],PrimeQ[#^2+27]&&PrimeQ[#+3]&];Through[{Total,Length}[p]]`

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

There is undoubtedly a much shorter way to do this.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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**phrontister****Real Member**- From: The Land of Tomorrow
- Registered: 2009-07-12
- Posts: 4,592

But I thought your code was about as short as it could get!

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**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

That would be a piece of luck. M exposes all my weaknesses.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

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