## Open chess positions

### Problem 628 Published on Sunday, 3rd June 2018, 01:00 am; Solved by 483;Difficulty rating: 25%

A position in chess is an (orientated) arrangement of chess pieces placed on a chessboard of given size. In the following, we consider all positions in which $n$ pawns are placed on a $n \times n$ board in such a way, that there is a single pawn in every row and every column.

We call such a position an open position, if a rook, starting at the (empty) lower left corner and using only moves towards the right or upwards, can reach the upper right corner without moving onto any field occupied by a pawn.

Let $f(n)$ be the number of open positions for a $n \times n$ chessboard.
For example, $f(3)=2$, illustrated by the two open positions for a $3 \times 3$ chessboard below.

You are also given $f(5)=70$.

Find $f(10^8)$ modulo $1\,008\,691\,207$.