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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 4 |
| 3 | 36 |
| 4 | 336 |
| 5 | 3840 |
| 6 | 52800 |
| 7 | 836640 |
| 8 | 14864640 |
| 9 | 291755520 |
| 10 | 6264276480 |
| 11 | 145962432000 |
| 12 | 3665362821120 |
| 13 | 98604459233280 |
| 14 | 2827182573895680 |
| 15 | 86016204578304000 |
| 16 | 2766450467708928000 |
| 17 | 93741871082943283200 |
| 18 | 3336807307530977280000 |
| 19 | 124443669133537276723200 |
[1,0,4,36,336,3840,52800,836640,14864640, 291755520,6264276480,145962432000,3665362821120, 98604459233280,2827182573895680,86016204578304000, 2766450467708928000,93741871082943283200, 3336807307530977280000,124443669133537276723200] |