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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 12 |
| 3 | 69 |
| 4 | 504 |
| 5 | 4440 |
| 6 | 45720 |
| 7 | 538020 |
| 8 | 7116480 |
| 9 | 104455008 |
| 10 | 1684005120 |
| 11 | 29571696000 |
| 12 | 561695238720 |
| 13 | 11472451848000 |
| 14 | 250694772007680 |
| 15 | 5835284153899200 |
| 16 | 144124039400140800 |
| 17 | 3764378233282867200 |
| 18 | 103661897106414366720 |
| 19 | 3001493647870874956800 |
[1,3,12,69,504,4440,45720,538020,7116480, 104455008,1684005120,29571696000,561695238720, 11472451848000,250694772007680,5835284153899200, 144124039400140800,3764378233282867200, 103661897106414366720,3001493647870874956800] |