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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 40 |
| 4 | 796 |
| 5 | 27196 |
| 6 | 1437136 |
| 7 | 108931264 |
| 8 | 11207616400 |
| 9 | 1502077491856 |
| 10 | 254091983968576 |
| 11 | 52922687300496256 |
| 12 | 13303823750214614464 |
| 13 | 3970706309867394765760 |
| 14 | 1387875547214097148600576 |
| 15 | 561507863501525383223535616 |
| 16 | 260328000140228961840632033536 |
[1,1,4,40,796,27196,1437136,108931264,11207616400, 1502077491856,254091983968576,52922687300496256, 13303823750214614464,3970706309867394765760, 1387875547214097148600576, 561507863501525383223535616, 260328000140228961840632033536] |