Number happening to get noticed outside (9)
I believe the answer is:
seventeen
'number' is the definition.
(seventeen is a kind of whole number)
'happening to get noticed outside' is the wordplay.
'happening' becomes 'event' (I've seen this in another clue).
'to get noticed' becomes 'seen' (I can't justify this - if you can you should believe this answer much more).
'outside' indicates putting letters inside.
'event' going inside 'seen' is 'SEVENTEEN'.
Can you help me to learn more?
(Other definitions for seventeen that I've seen before include "Quite a few" , "Figure" , "odd number" , "next clue" , "XVII" .)