Declared a number was incorrect (7)
I believe the answer is:
averred
'declared' is the definition.
(averring is a kind of declaring)
'a number was incorrect' is the wordplay.
'number' becomes 'v' (V is an example).
'was incorrect' becomes 'erred' (I've seen this before).
'a'+'v'+'erred'='AVERRED'
(Other definitions for averred that I've seen before include "Stated, asserted" , "Stated to be the case" , "Alleged, asserted" , "Asserted to be the case" , "confidently stated" .)