Number of Columns: 3
Number of Rows	Total Solutions
3	0
4	0
5	0
6	0
7	6
8	24
9	60
10	120
11	210
12	336
13	504
14	720
15	990
16	1,320
17	1,716
18	2,184
19	2,730
20	3,360
21	4,080
22	4,896
23	5,814
24	6,840
25	7,980
26	9,240
27	10,626
28	12,144
29	13,800
30	15,600

Equation (where "r" is the number of rows):

solutions = (r-6)*(r-5)*(r-4)

for r > 6