A large useless collection of numbers (5)
I believe the answer is:
album
'collection of numbers' is the definition.
'album' can be an answer for 'collection' (I have seen 'Collection of photographs' mean 'album' so perhaps 'collection' could also mean 'album'). I'm not certain of the 'of numbers' bit.
'a large useless' is the wordplay.
'large' becomes 'L' (eg in clothes sizes).
'useless' becomes 'bum' (I've seen this in other clues).
'a'+'l'+'bum'='ALBUM'
Can you help me to learn more?
(Other definitions for album that I've seen before include "Cuttings book" , "Music record or photo book" , "Blank book for keeping stamps, photographs etc" , "Book for, eg, stamps" , "Record with multiple tracks" .)