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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 8 |
| 4 | 46 |
| 5 | 340 |
| 6 | 3080 |
| 7 | 33020 |
| 8 | 408760 |
| 9 | 5737600 |
| 10 | 90041480 |
| 11 | 1562155760 |
| 12 | 29688699040 |
| 13 | 613378208080 |
| 14 | 13687826477600 |
| 15 | 328103392918400 |
| 16 | 8407745335871200 |
| 17 | 229363476365320000 |
| 18 | 6636554484183747200 |
| 19 | 203007064284501963200 |
| 20 | 6545704564601880726400 |
| 21 | 221887453210925123353600 |
[1,1,2,8,46,340,3080,33020,408760,5737600, 90041480,1562155760,29688699040,613378208080, 13687826477600,328103392918400,8407745335871200, 229363476365320000,6636554484183747200, 203007064284501963200,6545704564601880726400, 221887453210925123353600] |