1.11|

$ cd ~

SICP Exercise 1.11

Recursive:

(define (f n)
  (cond ((< n 3) n)
      (else (+ (f (- n 1))
               (* 2 (f (- n 2)))
               (* 3 (f (- n 3)))))))

Iterative:

 (define (f n) 
   (define (iter a b c count) 
     (if (= count 0) 
       a 
       (iter b c (+ c (* 2 b) (* 3 a)) (- count 1)))) 
   (iter 0 1 2 n))