I didn't realize that Chez Scheme lacked arbitrary precision reals. The following can compute the rational values fairly easily for Task 1. What Scheme implementations do have arbitrary precision reals, just out of curiosity.
(def-memo (v n)
(case n
((1) 2)
((2) -4)
(else
(+ 111 (/ -1130 (v (- n 1))) (/ 3000 (* (v (- n 1)) (v (- n 2))))))))