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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 12 |
| 4 | 66 |
| 5 | 450 |
| 6 | 3510 |
| 7 | 32760 |
| 8 | 335160 |
| 9 | 3832920 |
| 10 | 48648600 |
| 11 | 673596000 |
| 12 | 9961736400 |
| 13 | 161026866000 |
| 14 | 2775402630000 |
| 15 | 50713246584000 |
| 16 | 987048958896000 |
| 17 | 20331148966128000 |
| 18 | 440625863806128000 |
| 19 | 10057578887708352000 |
| 20 | 240218186856167520000 |
| 21 | 6010719623406257760000 |
[1,1,3,12,66,450,3510,32760,335160,3832920, 48648600,673596000,9961736400,161026866000, 2775402630000,50713246584000,987048958896000, 20331148966128000,440625863806128000, 10057578887708352000,240218186856167520000, 6010719623406257760000] |