Na2a and lucky stone

A number is called as a lucky number if its decimal representation contains only the lucky digits, 4 and 7. e.g. 47, 744, 4 are lucky numbers, whereas 5, 17, 467 are not. Recently, Na2a found a magic stone. With the help of this stone, he can multiply a number by any lucky number. Also, the magic stone can be used any number of times (possibly zero or infinite number of times). For example, if in