| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 18 |
| 4 | 324 |
| 5 | 9140 |
| 6 | 359460 |
| 7 | 18408600 |
| 8 | 1174201280 |
| 9 | 90423766800 |
| 10 | 8215991163000 |
| 11 | 865420074120800 |
| 12 | 104218992780067440 |
| 13 | 14188585798246317120 |
| 14 | 2163608674997595229040 |
| 15 | 366682177870608886473600 |
| 16 | 68611838511981521881152000 |
| 17 | 14093827998013078645611495680 |
[1,2,18,324,9140,359460,18408600,1174201280, 90423766800,8215991163000,865420074120800, 104218992780067440,14188585798246317120, 2163608674997595229040,366682177870608886473600, 68611838511981521881152000, 14093827998013078645611495680] |