Find the sum upto n terms of the series `1+4+7+10+13+16+"...."`.

Explanation

To find the sum up to \( n \) terms of the series \( 1 + 4 + 7 + 10 + 13 + 16 + \ldots \), we can follow these steps:

### Step 1: Identify the first term and common difference
The first term of the series \( a_1 \) is \( 1 \) (the first number in the series), and the second term \( a_2 \) is \( 4 \).

To find the common difference \( d \):
\[
d = a_2 - a_1 = 4 - 1 = 3
...