## 16 Replies - 1021 Views - Last Post: 21 March 2009 - 08:53 AM

### #1

# Need help for this project Please!

Posted 20 March 2009 - 08:38 AM

Write a Java program that calculates the following product.

(1+1/2^2) (1+1/3^2)(1+1/5^2)(1+1/7^2).....(1+1/(P(n))^2)

the #s 2,3,4,5,....Pn are the 1st primes. Prompt the user to enter the integer n. Print the result as a double value. use dialog boxes for input/output perations.

can anyone give me any suggestion?

is there any formular can do this problem?

Thank you very much!

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**Replies To:** Need help for this project Please!

### #2

## Re: Need help for this project Please!

Posted 20 March 2009 - 08:41 AM

### #3

## Re: Need help for this project Please!

Posted 20 March 2009 - 08:50 AM

http://www.computing...java/11287.html

static public IsPrime(int number) { if (number == 1 || number == 2) return 1; for (int i=2; i<(int)(number/2); i++)//assumes number is unsigned...I don't even know that you *can* have unsigned numbers in Java...in either case, I'm sure there's a Math.abs() or something similar that you could use { if ( (number/i)==(int)(number/i) ) return 0; } return 1; }

### #4

## Re: Need help for this project Please!

Posted 20 March 2009 - 08:50 AM

mostyfriedman, on 20 Mar, 2009 - 07:41 AM, said:

I know how to generate the prime number ( kind of)

but I dont know how to put them together ... i mean I dont know how to do the rest part of it. my mind is not clear I guess, I will go back to think again.

anyway thank you

### #5

## Re: Need help for this project Please!

Posted 20 March 2009 - 09:02 AM

Quote

do you mean you don't know how to print to screen or do do calculations in java?

### #6

## Re: Need help for this project Please!

Posted 20 March 2009 - 09:08 AM

scottyadam, on 20 Mar, 2009 - 08:02 AM, said:

Quote

do you mean you don't know how to print to screen or do do calculations in java?

thanks for reply

I meant that I dont know how to do the calculations..I kept think there should be a fomular for that equation...

### #7

## Re: Need help for this project Please!

Posted 20 March 2009 - 09:22 AM

scottyadam, on 20 Mar, 2009 - 07:50 AM, said:

http://www.computing...java/11287.html

static public IsPrime(int number) { if (number == 1 || number == 2) return 1; for (int i=2; i<(int)(number/2); i++)//assumes number is unsigned...I don't even know that you *can* have unsigned numbers in Java...in either case, I'm sure there's a Math.abs() or something similar that you could use { if ( (number/i)==(int)(number/i) ) return 0; } return 1; }

there's a more efficient way to do this btw

### #8

## Re: Need help for this project Please!

Posted 20 March 2009 - 09:56 AM

public static boolean isPrime(int num){ if (num == 1) return false; // Not prime for( int i = 2; i < num; i++ ) { if (num % i == 0) return false; // Not prime if (num % i != 0) return true; // Prime } return false; // won't reach here }

you might wanna do something like this for the calculations....I don't know if this would even work cause I hacked it out pretty fast....

for( int i = number; i > 2; i-- ){ if(isPrime(i)){ answer = ( (1+1)/( Math.pow( 2, i) ) ); } }

### #9

## Re: Need help for this project Please!

Posted 20 March 2009 - 09:59 AM

scottyadam, on 20 Mar, 2009 - 08:56 AM, said:

public static boolean isPrime(int num){ if (num == 1) return false; // Not prime for( int i = 2; i < num; i++ ) { if (num % i == 0) return false; // Not prime if (num % i != 0) return true; // Prime } return false; // won't reach here }

you might wanna do something like this for the calculations....I don't know if this would even work cause I hacked it out pretty fast....

for( int i = number; i > 2; i-- ){ if(isPrime(i)){ answer = ( (1+1)/( Math.pow( 2, i) ) ); } }

the isPrime() wont work for some cases actually

### #10

## Re: Need help for this project Please!

Posted 20 March 2009 - 10:05 AM

which ones....

at a quick glance how does the rest look?

OR BETTER YET...since I kinda came up with this...maybe i'll let jinggessler find out what's wrong...that way jinggessler can better understand what's going on :-) (put this into a SSCCE and your in business!!)

SSCCE - Short Self-Contained Compilable Example

This post has been edited by **scottyadam**: 20 March 2009 - 10:13 AM

### #11

## Re: Need help for this project Please!

Posted 20 March 2009 - 10:13 AM

### #12

## Re: Need help for this project Please!

Posted 20 March 2009 - 11:59 AM

So instead of i++ing , cut the process in half with i+=2.

Just my opinion

EDIT:

A little bit more detail,

if(num == 2) return true; else if(num%2==0) return false; //then check for all the odds.

This post has been edited by **DillonSalsman**: 20 March 2009 - 12:04 PM

### #13

## Re: Need help for this project Please!

Posted 20 March 2009 - 12:13 PM

### #14

## Re: Need help for this project Please!

Posted 20 March 2009 - 12:17 PM

public static boolean isPrime(int n) { if( n == 2 ) return true; if( n < 2 || n % 2 == 0 ) return false; for(int i = 3; i*i <= n; i += 2) { if( n % i == 0 ) return false; } return true; }

### #15

## Re: Need help for this project Please!

Posted 20 March 2009 - 03:39 PM

I want to thank all your help, I will use all your advices to rework on my project again.

Thank you Thank you!!