# Question regarding sequence and series

Algebra Level pending

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 $$r>1$$.

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

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