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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 15 |
| 3 | 111 |
| 4 | 1116 |
| 5 | 14352 |
| 6 | 226176 |
| 7 | 4233492 |
| 8 | 91936080 |
| 9 | 2274815712 |
| 10 | 63220205736 |
| 11 | 1950659365608 |
| 12 | 66187523184048 |
| 13 | 2450020566119760 |
| 14 | 98269427218682880 |
| 15 | 4246150991775421824 |
| 16 | 196657057172519603712 |
| 17 | 9719485198364207149056 |
| 18 | 510628699670802850684800 |
[1,3,15,111,1116,14352,226176,4233492,91936080, 2274815712,63220205736,1950659365608, 66187523184048,2450020566119760,98269427218682880, 4246150991775421824,196657057172519603712, 9719485198364207149056,510628699670802850684800] |