IF R.A.H.M.A.N. is to be true

Then;

1st PM: Tunku Abdul Rahman
2nd PM: Tun ............Abdul Razak
3rd PM: Tun ...........Hussein Onn
4th PM: Tun Dr. ......Mahathir Mohamad
5th PM: Dato' Seri ....Abdullah Ahmad Badawi
6th PM: (Title) ........N

Who would the N be? Najib? Nazri? Or other people that name start with N?