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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 20 |
| 5 | 148 |
| 6 | 1348 |
| 7 | 15104 |
| 8 | 198144 |
| 9 | 2998656 |
| 10 | 51290496 |
| 11 | 979732224 |
| 12 | 20661458688 |
| 13 | 476936766720 |
| 14 | 11959743432960 |
| 15 | 323764901314560 |
| 16 | 9410647116349440 |
| 17 | 292316310979706880 |
| 18 | 9663569062008422400 |
| 19 | 338760229843058688000 |
[1,1,4,20,148,1348,15104,198144,2998656,51290496, 979732224,20661458688,476936766720,11959743432960, 323764901314560,9410647116349440, 292316310979706880,9663569062008422400, 338760229843058688000] |