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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 24 |
| 5 | 120 |
| 6 | 840 |
| 7 | 5880 |
| 8 | 54600 |
| 9 | 491400 |
| 10 | 5276880 |
| 11 | 58045680 |
| 12 | 749770560 |
| 13 | 9747017280 |
| 14 | 142685262720 |
| 15 | 2140278940800 |
| 16 | 35879056012800 |
| 17 | 609943952217600 |
| 18 | 11334678568012800 |
| 19 | 215358892792243200 |
| 20 | 4453151976335462400 |
| 21 | 93516191503044710400 |
| 22 | 2108447155238693068800 |
[0,1,3,24,120,840,5880,54600,491400,5276880, 58045680,749770560,9747017280,142685262720, 2140278940800,35879056012800,609943952217600, 11334678568012800,215358892792243200, 4453151976335462400,93516191503044710400, 2108447155238693068800] |