This may be controversial, but in my opinion, you can only be a 4, or an ENTP, but not both. Any enneagram type is possible in theory, but in practice 4 as a core type goes against the very essence of being an ENTP.I'm an ENTP and identify most with 4, 5, and 7, in that order. I've never heard of another ENTP 4 though, so I might be an oddity.
Switch around 4 and 2, and 8 and 9. 4 doesn't fit Fe too well (my own 4ishness isn't exactly a healthy configuration of it), and Fast-9 seems to fit better than 8 (ENTP similarly isn't the most choleric type ever, and fast-9 is often mistaken for 7w6).I believe that there is some correlation, but nothing is exclusive. There's nothing to say that one MBTI type cannot be a particular Enneagram type.
With that said, in my experience, most ENTPs are 7, 3, or 8 in that order of regularity. Within each section (gut,head,heart), I'd order them like this:
Gut: 8, 9, 1
Head: 7, 6, 5
Heart: 3, 4, 2
(In order of most common to least.)
Of course, that's just my personal assessment.