Exercise 4 Page 447

The given rule means that, after the first term of the sequence, every term $a_n$ is the difference between the previous term $a_{n-1}$ and $5.$

$a_1=1,$ $a_2=\text{-}4,$ $a_3=\text{-}9,$ $a_4=\text{-}14,$ $a_5=\text{-}19,$ $a_6=\text{-}24$