You are not logged in.

- Topics: Active | Unanswered

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,606

Here is a problem I found on brilliant.org

Consider all 3-term geometric sequences with first term 1 and with common ratio the square of an integer between 1 and 1000 (inclusive). How many of these 1000 geometric sequences have the property that the sum of the 3 terms is prime?

I wrote this M code to do it:

`Select[Table[1+q^2+q^4,{q,1,Floor[Sqrt[1000]]}],PrimeQ[#]&]//Length`

but I am suspecting there is a better way to do it. Does anyone know of a better and/or shorter way to do it?

*Last edited by anonimnystefy (2013-04-30 03:49:56)*

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 88,898

Hi;

**In mathematics, you don't understand things. You just get used to them.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

**Online**

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,606

I haven't noticed that at all. I was focused on finding an M only solution.

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 88,898

Hi;

The M solution is fine. There might be a faster way but in this case the CSBFC principle applies.

**In mathematics, you don't understand things. You just get used to them.**

**I agree with you regarding the satisfaction and importance of actually computing some numbers. I can't tell you how often I see time and money wasted because someone didn't bother to run the numbers.**

**Online**

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,606

Csbfc?

Here lies the reader who will never open this book. He is forever dead.

Taking a new step, uttering a new word, is what people fear most. ― Fyodor Dostoyevsky, Crime and Punishment

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 88,898

Nope, CSBFC.

**In mathematics, you don't understand things. You just get used to them.**

**Online**

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,606

That is what I wrote, but the forum tirns it lower case automatically. What does that acronym mean?

Here lies the reader who will never open this book. He is forever dead.

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 88,898

CommonSense, Brute Force and the Computer.

**In mathematics, you don't understand things. You just get used to them.**

**Online**

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,606

Sound like a good name for a book.

Here lies the reader who will never open this book. He is forever dead.

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 88,898

Not a book, a dynamite article though.

**In mathematics, you don't understand things. You just get used to them.**

**Online**

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,606

Sure. Why not!

By the way, I like your new avatar.

Here lies the reader who will never open this book. He is forever dead.

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 88,898

It already happened and I was the only person who read it.

**In mathematics, you don't understand things. You just get used to them.**

**Online**

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,606

The only mention of that article on the Internet is on this forum by you. I am guessing you are the guy who never got it published?

Here lies the reader who will never open this book. He is forever dead.

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 88,898

Hmmmm, it appears you did not read everything I said about that article.

**In mathematics, you don't understand things. You just get used to them.**

**Online**

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,606

Yes, I did.

Here lies the reader who will never open this book. He is forever dead.

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 88,898

bobbym wrote:

A brilliant guy I knew wrote an article for a famous computer journal called

"Common Sense, Brute Force and the Computer." It did not get published and it

was a really great article.

We have already established in the other thread that though I may look brilliant and smell brilliant, I am not brilliant,

**In mathematics, you don't understand things. You just get used to them.**

**Online**

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,606

We established exactly the opposite.

Here lies the reader who will never open this book. He is forever dead.

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 88,898

I am afraid that it is difficult to establish assertions that are untrue.

The author was brilliant, I am not, therefore I am not the author.

**In mathematics, you don't understand things. You just get used to them.**

**Online**

**pgoh63****Member**- Registered: 2013-05-02
- Posts: 2

I need help to find the nth for this sequence :

1, 1, 3/4, 1/2, 5/16

Pls help.

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 88,898

Hi pgoh63;

Where does the sequences come from? There are a lot of possible fits for it.

**In mathematics, you don't understand things. You just get used to them.**

**Online**

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,606

Hi pgoh63

I am getting 3/16 as the next term.

Here lies the reader who will never open this book. He is forever dead.

Offline

**pgoh63****Member**- Registered: 2013-05-02
- Posts: 2

I got this from my girl's school homework. Not sure if there is any typo errors....I also suspect the fifth term might be wrong. Will check with the school teacher.

Offline

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,606

Hi pgoh63

Have you seen my answer?

Here lies the reader who will never open this book. He is forever dead.

Offline

**bobbym****Administrator**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 88,898

Is it the same answer if the fifth term is wrong?

**In mathematics, you don't understand things. You just get used to them.**

**Online**

**anonimnystefy****Real Member**- From: The Foundation
- Registered: 2011-05-23
- Posts: 15,606

Maybe and maybe not. Until he posts the correct fifth term we cannot know.

But it seems he got that idea because you said there were many possible fits.

Here lies the reader who will never open this book. He is forever dead.

Offline