Question regarding sequence and series

If $a_1, a_2, a_3, \ldots , a_n$ are in an arithmetic progression with first term $a$ and common difference $d$ , find the sum below for $r>1$ .

$( a_1 a_2 \cdots a_r )+(a_2 a_3 \cdots a_{r+1}) + (a_3 a_4 \cdots a_{r+2} )+ \cdots +(a_n a_{n+1} \cdots a_{r+n-1})$