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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 5 |
| 4 | 20 |
| 5 | 116 |
| 6 | 696 |
| 7 | 5016 |
| 8 | 40128 |
| 9 | 361152 |
| 10 | 3611520 |
| 11 | 39899520 |
| 12 | 478794240 |
| 13 | 6226813440 |
| 14 | 87175388160 |
| 15 | 1307630822400 |
| 16 | 20922093158400 |
| 17 | 355686731366400 |
| 18 | 6402361164595200 |
| 19 | 121645087867699200 |
| 20 | 2432901757353984000 |
[0,0,1,5,20,116,696,5016,40128,361152,3611520, 39899520,478794240,6226813440,87175388160, 1307630822400,20922093158400,355686731366400, 6402361164595200,121645087867699200, 2432901757353984000] |