a(n,k)  tabf head (staircase) for  A091746


   n\k           2            3            4            5           6          7         8        9     10     11     12

                      
   1             1            0            0            0           0          0         0        0      0      0      0
                       
   2            30           12            1            0           0          0         0        0      0      0      0
                      
   3          2700         1920          426           36           1          0         0        0      0      0      0
                      
   4        491400       478800       162540        25344        1956         72         1        0      0      0      0
                  
   5     150368400    181440000     80451000     17624880     2130660     147840      5820      120      1      0      0
          
   6   69470200800  98424849600  52905560400  14618016000  2346624000  232202880  14513940   571200  13650    180      1
                                                                     

   The sequence of row lengths for this array is [1,3,5,7,9,11,...]=A005408(n-1), n>=1.