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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 12 |
| 5 | 286 |
| 6 | 33592 |
| 7 | 23178480 |
| 8 | 108995910720 |
| 9 | 3973186258569120 |
[1,1,2,12,286,33592,23178480,108995910720, 3973186258569120] |