(define (f n)
  (define v (make-vector (+ 1 n) #f))
  (define (get i)
    (vector-ref v i))
  (define (set i x)
    (vector-set! v i x) x)
  (define (g n)
    (or
     (get n)
     (cond
      ((= n 0) (set 0 4))
      ((= n 1) (set 1 (/ 17 4)))
      (else (set n (+ (- 108 (/ 815 (g (- n 1)))) (/ 1500 (* (g (- n 1)) (g (- n 2))))))))))
  (g n))
(define (p e)
  (print (list e (exact->inexact e))))
(p (f 0))
(p (f 1))
(p (f 2))
(p (f 3))
(p (f 80))