Definition:Multiply Perfect Number/Linguistic Note
Linguistic Note on Multiply Perfect Number
Note that the word multiply in the term multiply perfect number is an adverb: a word that qualifies an adjective.
As such it should be interpreted as multiple-ly, that is, in the form of being a multiple, and is pronounced something like mul-ti-plee.
Do not confuse with the verb form of multiply, meaning to perform an act of multiplication, which is pronounced something like mul-ti-pligh.