Find sum to n terms of the series `1+(2+3)+(4+5+6)+"...."`.

Explanation

To find the sum of the series \( S_n = 1 + (2 + 3) + (4 + 5 + 6) + \ldots \) up to \( n \) terms, we can break down the problem step by step.

### Step 1: Identify the pattern of the series
The series can be seen as:
- The first term is \( 1 \) (which is \( 1 \))
- The second term is \( 2 + 3 \) (which is \( 5 \))
- The third term is \( 4 + 5 + 6 \) (which is \( 15 \))
- The fourth term is \( 7 + 8 + 9 + 10 \) (which is \( 34 \))
...