A4O-SO —

This is a shortened 747 belonging to Oman's Royal flight. Being such a large country it also has one 747-400 and a 747-8 plus assorted smaller craft so the Sultan and dignataries can travel all over the world several times a year to attend high level meetinds..

Looks like an old PanAm 747SP.

https://en.wikipedia.org/wiki/Boeing_747SP

Oman is a large country?

I'm guessing @chalet's comment contains a touch of sarcasm...

Originally delivered to Braniff, this s one of the few SP's still flying, the horrible looking bump on the top houses communications equipment.

747SP, A40-SO: Originally owned by Braniff (a BIG ORANGE), first flight 1979-10-07, sold back to Boeing 1981--01-23, sold to Oman Government 1984-07-02, but, never apparently titled thru current day.
Large communications dome installed on the spine 1984-10-01.
Last reported fight to date 2018-06-19, HAMburg to Oman's MCT Muscat Airport.
http://www.747sp.com/747sp-production-list/21785-405/

Thanks Robert Mills Jr for the details!

With all their money I'm surprised the Sultan is still flying around in this old bird. Probably ready for a trade in. 787-9 maybe?

Could also be an old Qantas 747SP, they were highly sought after when sold.