\[1)\ P_{6} = 6! = 6 \bullet 5 \bullet 4 \bullet 3 \bullet 2 = 720;\]
\[2)\ P_{8} = 8! = 8 \bullet 7 \bullet 6 \bullet 5 \bullet 4 \bullet 3 \bullet 2 =\]
\[= 40\ 320;\]
\[3)\ P_{7} = 7! = 7 \bullet 6 \bullet 5 \bullet 4 \bullet 3 \bullet 2 =\]
\[= 5040;\]
\[4)\ P_{9} = 9! = 9 \bullet 8 \bullet 7 \bullet 6 \bullet 5 \bullet 4 \bullet 3 \bullet 2 =\]
\[= 362\ 880.\]