| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 36 |
| 4 | 560 |
| 5 | 8160 |
| 6 | 116192 |
| 7 | 1638336 |
| 8 | 23006720 |
| 9 | 322513920 |
| 10 | 4517714432 |
| 11 | 63263118336 |
| 12 | 885774356480 |
| 13 | 12401385185280 |
| 14 | 173622657769472 |
| 15 | 2430736799809536 |
| 16 | 34030432743587840 |
| 17 | 476426763687690240 |
| 18 | 6669978923292557312 |
| 19 | 93379730316084903936 |
| 20 | 1307316376765123788800 |
[0,0,2,36,560,8160,116192,1638336,23006720, 322513920,4517714432,63263118336,885774356480, 12401385185280,173622657769472,2430736799809536, 34030432743587840,476426763687690240, 6669978923292557312,93379730316084903936, 1307316376765123788800] |