Problem 10
Statement
The sum of the primes below 10 is 2 + 3 + 5 + 7 = 17.
Find the sum of all the primes below two million.
Solution
The code, in C.
#include <stdio.h>
unsigned long long int primeSum(int l)
{
int a[l+1];
unsigned long long int b,c;
unsigned long long int s=0;
for(b=0;b<=l;b++)
a[b]=1;
a[0]=0;
a[1]=0;
for(c=2;c<1800;){
for(b=c+1;b<=l;b++)
if(b%c==0) a[b]=0;
for(b=c+1;b<=1800;b++){
c=l;
if(a[b]==1){
c=b;
break;
}
}
}
for(b=0;b<=l;b++)
if(a[b])
s+=b;
return s;
}
int main(void)
{
printf("%llu\n",primeSum(2000000));
return 0;
}
Answer
142913828922
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