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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 3 |
| 4 | 7 |
| 5 | 24 |
| 6 | 117 |
| 7 | 663 |
| 8 | 4824 |
| 9 | 40367 |
| 10 | 381554 |
| 11 | 4001849 |
| 12 | 46043780 |
| 13 | 576018785 |
| 14 | 7783281188 |
| 15 | 112953364381 |
| 16 | 1752128923245 |
| 17 | 28930230194371 |
| 18 | 506596534953769 |
[1,3,7,24,117,663,4824,40367,381554,4001849, 46043780,576018785,7783281188,112953364381, 1752128923245,28930230194371,506596534953769] |