Generate series and show sum of 1*3*5 + 2*5*8 + 3*7*11

Question

Generating series using Java,

1*3*5 + 2*5*8 + 3*7*11......

And show the sum.

I tried this way, but didn't work. Any better algorithm to generate this series?

    public static void main(String[] args) {


     int sum1 = 1;
     int sum2 = 0;
     int sum3 = 0;
     int num = 0;;
     for(int i=1; i<5; i++) {
         for(int j=1; j<3; j++) {
             for(int k=1; k <= i+1; k++) {

                 num++;
             }

             sum1 *= num; 
         }

         sum2 += sum1; 
     }
}

Answer 1

Since you need to generate the sum of a series of N elements, you only need a single loop (no need for nested loops).

You should notice that the elements of the series can be computed as:

Element(1) = 1 * 3 * 5
...
Element(i) = i * j * k
Element(i+1) = (i+1) + (j+2) * (k+3)

Therefore, you can use 3 variables to calculate the current element to be added to the sum.

int sum = 0;
int j = 3;
int k = 5;
for(int i = 1; i <= N; i++) {
    sum += i * j * k;  
    j+=2;
    k+=3;
}

or

int sum = 0;
for(int i = 1, j = 3, k = 5; i <= N; i++, j+=2, k+=3) {
    sum += i * j * k;  
}

Answer 2

You can try the next simple code

public static void main(String[] args) {
    // TODO Auto-generated method stub
    int sum1 = 0;
     int sum2 = 0;
     int sum3 = 0;
     int num = 0;
     int series = 10;
     int result = 0;
     for(int i=1; i<series; i++){
        sum1 = i;
        sum2 = sum1+sum1+1;
        sum3 = sum2+sum1+1;
        System.out.print(sum1+"*"+sum2+"*"+sum3+"+");
        result += sum1 * sum2 * 3;
     }
     System.out.print("Final result: "+result);
}

Answer 3

You should be able to do it in one loop like this

public static void main(String args[]){
    int first = 1;
    int second = 3;
    int third = 5;
    int n = 5;
    int sum  = 0;
    for(int i=0;i<n;i++){
        sum+=first*second*third;
        first++;
        second+=2;
        third+=3;
    }
}

Answer 4

for (i = 1; i <= limit; i++) {
    sum += (i * (i+i+1) * (i+i+i+2))
}

I have assumed this logic :

1 : [1] * ([1] + 2) * (([1] + 2) + 2)

2 : [2] * ([2] + 3) * (([2] + 3) + 3)

3 : [3] * ([3] + 4) * (([3] + 4) + 4)

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