This number's dry without singer's introduction (6)

I believe the answer is:

thirty

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'this number's' is the definition.
(thirty is a kind of whole number)

I don't understand the remainder of the clue.

(Other definitions for thirty that I've seen before include "The number of silver coins for betrayal" , "Days in September, April, June and November" , "Score and a half" , "Half of threescore" , "Both RU teams" .)

I've seen this clue in The Independent.

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