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| n | a(n) |
|---|---|
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 6 |
| 6 | 24 |
| 7 | 80 |
| 8 | 312 |
| 9 | 1152 |
| 10 | 4616 |
| 11 | 18384 |
| 12 | 77280 |
| 13 | 328352 |
| 14 | 1451712 |
| 15 | 6527616 |
| 16 | 30299504 |
| 17 | 143322000 |
| 18 | 696359232 |
| 19 | 3448656512 |
| 20 | 17483842176 |
| 21 | 90301959744 |
| 22 | 476270369600 |
| 23 | 2557007766912 |
| 24 | 13991998520832 |
| 25 | 77867819879936 |
| 26 | 441003737739264 |
| 27 | 2537848321044480 |
| 28 | 14843836828748672 |
[0,0,2,6,24,80,312,1152,4616,18384,77280,328352, 1451712,6527616,30299504,143322000,696359232, 3448656512,17483842176,90301959744,476270369600, 2557007766912,13991998520832,77867819879936, 441003737739264,2537848321044480, 14843836828748672] |