A farmer has some number of sheep and needs to divide them into equal groups.

He tries groups of 2, but finds he has 1 left over.

Then he tries groups of 3, but has 2 left over.

Then he tries groups of 4, but has 3 left over.

And so on, until he gets to groups of 17, and the sheep fit perfectly.

What is the minimum number of sheep he has?