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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 9 |
| 5 | 30 |
| 6 | 88 |
| 7 | 240 |
| 8 | 624 |
| 9 | 1568 |
| 10 | 3840 |
| 11 | 9216 |
| 12 | 21760 |
| 13 | 50688 |
| 14 | 116736 |
| 15 | 266240 |
| 16 | 602112 |
| 17 | 1351680 |
| 18 | 3014656 |
| 19 | 6684672 |
| 20 | 14745600 |
| 21 | 32374784 |
| 22 | 70778880 |
| 23 | 154140672 |
| 24 | 334495744 |
| 25 | 723517440 |
| 26 | 1560281088 |
| 27 | 3355443200 |
| 28 | 7197425664 |
| 29 | 15401484288 |
| 30 | 32883343360 |
[0,0,0,2,9,30,88,240,624,1568,3840,9216,21760, 50688,116736,266240,602112,1351680,3014656, 6684672,14745600,32374784,70778880,154140672, 334495744,723517440,1560281088,3355443200, 7197425664,15401484288,32883343360] |