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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 3 |
| 4 | 14 |
| 5 | 40 |
| 6 | 254 |
| 7 | 1106 |
| 8 | 9400 |
| 9 | 56232 |
| 10 | 607392 |
| 11 | 4685472 |
| 12 | 61485984 |
| 13 | 585235872 |
| 14 | 9014205888 |
| 15 | 102480586560 |
| 16 | 1806461775360 |
| 17 | 23934358033920 |
| 18 | 473963802485760 |
| 19 | 7180611912944640 |
| 20 | 157539651679641600 |
| 21 | 2688528843644313600 |
| 22 | 64654185117092659200 |
[0,0,2,3,14,40,254,1106,9400,56232,607392,4685472, 61485984,585235872,9014205888,102480586560, 1806461775360,23934358033920,473963802485760, 7180611912944640,157539651679641600, 2688528843644313600,64654185117092659200] |