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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 28 |
| 4 | 320 |
| 5 | 5556 |
| 6 | 129600 |
| 7 | 3756936 |
| 8 | 132872192 |
| 9 | 5679982288 |
| 10 | 286769980416 |
| 11 | 16732506817280 |
| 12 | 1115928688967680 |
| 13 | 84383735744758464 |
| 14 | 7163164003950936064 |
| 15 | 676619301019539271040 |
| 16 | 70674282825174467215360 |
| 17 | 8117559039240651749888256 |
[1,1,4,28,320,5556,129600,3756936,132872192, 5679982288,286769980416,16732506817280, 1115928688967680,84383735744758464, 7163164003950936064,676619301019539271040, 70674282825174467215360,8117559039240651749888256] |