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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 12 |
| 5 | 70 |
| 6 | 454 |
| 7 | 3332 |
| 8 | 27552 |
| 9 | 254400 |
| 10 | 2598852 |
| 11 | 29125932 |
| 12 | 355455468 |
| 13 | 4693396656 |
| 14 | 66671326176 |
| 15 | 1013916648840 |
| 16 | 16436063079552 |
| 17 | 282920894841096 |
| 18 | 5153797995148296 |
| 19 | 99052313167391760 |
| 20 | 2003040751641857856 |
| 21 | 42513854724369719136 |
| 22 | 944959706480298199824 |
[1,0,0,2,12,70,454,3332,27552,254400,2598852, 29125932,355455468,4693396656,66671326176, 1013916648840,16436063079552,282920894841096, 5153797995148296,99052313167391760, 2003040751641857856,42513854724369719136, 944959706480298199824] |