What size are the tiles?
If they are 1 foot by 1 foot,
then it will take at least 17*20=340 of them
I say, "at least",
because you may have to start at the center of the room
(You will have to check whether best to start with
a single centered tile,
an edge between a pair, turned one way,
or 90 degrees,
or the four corners of four tiles in the center)
and cut tiles, all around the edge,
to avoid ending up with tiny strips along the edges.
That will waste a few tiles.
By the way, it is usually cheaper
to just buy a single piece of carpet,
off a roll,
than to buy tiles.