Problem with Queens and Pawns

[Antreas P. Hatzipolakis]

Consider an n X n chessboard. Place n queens in the cells of the first row,
namely in the cells (1,1), (2,1),..., (n,1), and [(n+1)/2] pawns in the
odd cells of the second row, namely in the cells (1,2), (3,2), (5,2), ...
Which is the number of the unattacked (by the queens) cells ?

Example: 5 X 5

                    ---------------------
                  5 |   |   | * |   |   |
                    ---------------------
                  4 | * |   | * |   | * |
                    ---------------------
                  3 |   |   |   |   |   |
                    ---------------------
                  2 | P |   | P |   | P |
                    ---------------------
                  1 | Q | Q | Q | Q | Q |
                    ---------------------
                      1   2   3   4   5

Q: queen, P: pawn, *: unattacked cell

I made some computations by hand, and here is a table:

n |  1 2 3 4 5 6  7  8  9 10 11 12 13 14 15 .....
__|______________________________________________
# |  0 0 0 2 4 7 10 14 19 24 30 36 44 51 60 .....


Formula ??

Antreas