[racket] what's wrong with my code?

I'm really stuck trying to figure this out.  Any pointers are useful!
Here's the problem:

f(n) = n if n<4
and
f(n) = f(n - 1) + 2f(n - 2) + 3f(n - 3) + 4f(n - 4) if n>= 4

Here's my solution so far -- any one know what I'm doing wrong?

(define (f n)

  (define (f-iter result i)
    (if (> i 4)
        result
        (f-iter (+ result (* i (- n i))) (+ i 1))
    )
  )

  (if (< n 4)
      n
      (f-iter 0 1)
  )

)

(f 4) ;; should produce 10, produces 10
(f 5) ;; should produce 26, produces 20
(f 6) ;; should produce 63, produces 30
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