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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 30 |
| 4 | 210 |
| 5 | 2310 |
| 6 | 29464 |
| 7 | 476928 |
| 8 | 9671392 |
| 9 | 222388792 |
| 10 | 6438663000 |
| 11 | 200560490130 |
| 12 | 7379606916000 |
| 13 | 299261862900000 |
| 14 | 13004421443456272 |
| 15 | 614231422273479360 |
| 16 | 31727029501157817600 |
| 17 | 1915248189055217892480 |
| 18 | 116762424492324428512272 |
[1,2,6,30,210,2310,29464,476928,9671392,222388792, 6438663000,200560490130,7379606916000, 299261862900000,13004421443456272, 614231422273479360,31727029501157817600, 1915248189055217892480,116762424492324428512272] |