Excel how to convert the allocation of values in a column, into values betwwen 1 to -1

Excel how to convert the allocation of values in a column, into values
betwwen 1 to -1

In Excel i've got column A values that are between 3-21. I want to convert
them in column B, in order to have the first value 3 = 1 and the last
value 21 = -1. Is this possible?
Thank you!