To attract a number break a rule (6)
I believe the answer is:
allure
'to attract' is the definition.
(I've seen this before)
'a number break a rule' is the wordplay.
'number' becomes 'l' (L is an example**).
'break' is an anagram indicator.
'rule' with letters rearranged gives 'lure'.
'a'+'l'+'lure'='ALLURE'
(Other definitions for allure that I've seen before include "Attractiveness, glamour" , "Enticement, attraction" , "Attraction, appeal" , "Tempt" , "Laurel (anag)" .)