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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 6 |
| 4 | 3 |
| 5 | 40 |
| 6 | 90 |
| 7 | 336 |
| 8 | 56 |
| 9 | 51840 |
| 10 | 226800 |
| 11 | 4435200 |
| 12 | 11975040 |
| 13 | 188697600 |
| 14 | 1210809600 |
| 15 | 100590336000 |
| 16 | 93405312000 |
| 17 | 23712495206400 |
| 18 | 2598365952000 |
| 19 | 6360528125952 |
| 20 | 3754478407680000 |
| 21 | 537799391281152000 |
| 22 | 802857662698291200 |
[1,1,6,3,40,90,336,56,51840,226800,4435200, 11975040,188697600,1210809600,100590336000, 93405312000,23712495206400,2598365952000, 6360528125952,3754478407680000,537799391281152000, 802857662698291200] |