/*An Efficient code to print all the sum of all numbers that are multiples of 3 & 5 below N.*/ #include int main(){ int t; printf("Enter number of times you want to try"); scanf("%d",&t); while(t--) { unsigned long long N,p=0,sum=0; printf("Enter the value of N "); scanf("%lld",&N); //Take input of N from user p = (N-1)/3; sum = ((3*p*(p+1))/2); p = (N-1)/5; sum = sum + ((5*p*(p+1))/2); p = (N-1)/15; sum = sum - ((15*p*(p+1))/2); printf("%lld\n", sum); //print the sum of all numbers that are multiples of 3 & 5 below N } return 0; }