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?