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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 24 |
| 4 | 130 |
| 5 | 960 |
| 6 | 9702 |
| 7 | 134512 |
| 8 | 2562516 |
| 9 | 67152240 |
| 10 | 2422643366 |
| 11 | 120395521752 |
| 12 | 8245524190254 |
| 13 | 778511553019200 |
| 14 | 101361018574446630 |
| 15 | 18202576574465956224 |
| 16 | 4509516189662784365688 |
| 17 | 1541444043912873505870464 |
| 18 | 727078284287957812245097914 |
[1,2,6,24,130,960,9702,134512,2562516,67152240, 2422643366,120395521752,8245524190254, 778511553019200,101361018574446630, 18202576574465956224,4509516189662784365688, 1541444043912873505870464, 727078284287957812245097914] |