Why do we name the IC from 74 like 7400, 7404 etc..?

Why do we name the IC from 74 like 7400, 7404 etc..?

7400 7402
mentions that it has dual inline package and 7 pins each side
4 represents number of gates last two digits r meant for type code
but number of gates for not gate ic not valid its called as 74 series ic’s