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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 24 |
| 4 | 273 |
| 5 | 3996 |
| 6 | 70785 |
| 7 | 1465506 |
| 8 | 34662222 |
| 9 | 921511944 |
| 10 | 27201024639 |
| 11 | 882828325530 |
| 12 | 31253560065684 |
| 13 | 1198758613494852 |
| 14 | 49530067909218819 |
| 15 | 2193498057583259784 |
| 16 | 103664556373964098860 |
| 17 | 5207896547115772335552 |
| 18 | 277161367378578537506868 |
[1,1,3,24,273,3996,70785,1465506,34662222, 921511944,27201024639,882828325530,31253560065684, 1198758613494852,49530067909218819, 2193498057583259784,103664556373964098860, 5207896547115772335552,277161367378578537506868] |