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November 26th, 2010, 02:34 PM   #1
 
Joined: Nov 2010
Posts: 1
List of numbers

How can I find/program a list of:
We only operate with natural numbers.

1. The prime numbers < 10 000
2. x = a^2 + b^2 < 10 000
3. x = a^3 + b^3 < 10 000
4. x = a^2 + b^2 + c^2 < 10 000
5. x = a^3 + b^3 + c^3 < 10 000

Thank you.
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December 3rd, 2010, 11:48 PM   #2
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Re: List of numbers

You could write such a program easily:
1. Use Eratosthene's sieve
2 and following: bound the values of a, b, c (obvious bounds) and test for all the possibilities within your boundaries
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February 16th, 2011, 09:09 AM   #3
 
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Posts: 3
Re: List of numbers

Code:
void q2(int x){
	int a,b;
	for(a=1;a<=71;a++)    //2*71^2 <= 10'000
		for(b=a;b<=71;b++)
			if (a*a+b*b==x)
				printf("%d %d\n",a,b);
}
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May 17th, 2012, 10:54 AM   #4
 
Joined: Feb 2011
Posts: 3
Re: List of numbers

Code:
#define N 10000
main() {
        int i, j, t[N]={0,0,1};
        for( i=3; i<N; i++ ) 
                t[i]=2;
        for( i=2; i<N; i++ )
                for( j=i+1; j<N; j++ )
                        t[j] = (t[j]*i) % j;
        for( i=0; i<N; i++ )
                if(t[i]) 
                        printf("%d ", i); }
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May 23rd, 2012, 09:09 AM   #5
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Re: List of numbers

This algorithm was improved over the years
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