I would take your animation and make a second one of just the part you want looped (3-9), which is easy in the Animation player.
In the Animation Player, select the animation keys you want to duplicate (all of them in 3-9) so they are selected. Then click the Edit button, and choose Duplicate Selection.
Now you have your original animation, and your new one, a copy that only contains frames 3-9 (as frames 0-6). Set that new animation to loop with the Animation Looping button.
Now dump frames 3-9 out of your original so it only contains the non-repeating frames.