A sum checked two ways

You will write the terms of an arithmetic progression and its sum by the formula, then check that the two agree.

Your tasks.

1. In ap_terms, return the list of the first n terms.
2. In ap_sum, return the sum of the first n terms by the formula $\dfrac{n}{2}[2a + (n - 1)d]$.
3. Set total to the sum of the first $30$ terms of $4, 9, 14, \ldots$, using your function.