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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 32 |
| 5 | 220 |
| 6 | 1592 |
| 7 | 11944 |
| 8 | 96000 |
| 9 | 847120 |
| 10 | 8209952 |
| 11 | 86020704 |
| 12 | 958326272 |
| 13 | 11243157952 |
| 14 | 138464594816 |
| 15 | 1789358629504 |
| 16 | 24250275913728 |
| 17 | 344002396594432 |
| 18 | 5092763802452480 |
| 19 | 78443316497892864 |
| 20 | 1253887341918199808 |
| 21 | 20761127890765634560 |
[0,1,2,6,32,220,1592,11944,96000,847120,8209952, 86020704,958326272,11243157952,138464594816, 1789358629504,24250275913728,344002396594432, 5092763802452480,78443316497892864, 1253887341918199808,20761127890765634560] |