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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 2 |
| 4 | 6 |
| 5 | 12 |
| 6 | 62 |
| 7 | 280 |
| 8 | 2380 |
| 9 | 22400 |
| 10 | 321776 |
| 11 | 5837608 |
| 12 | 146558244 |
| 13 | 4938979584 |
| 14 | 221994255984 |
| 15 | 13767288844128 |
| 16 | 1127789953750020 |
| 17 | 129161855009676368 |
| 18 | 19561367056434877784 |
| 19 | 4170365129835922726384 |
| 20 | 1181440903578343187882844 |
[1,1,2,2,6,12,62,280,2380,22400,321776,5837608, 146558244,4938979584,221994255984,13767288844128, 1127789953750020,129161855009676368, 19561367056434877784,4170365129835922726384, 1181440903578343187882844] |