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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 72 |
| 5 | 540 |
| 6 | 4680 |
| 7 | 46200 |
| 8 | 510720 |
| 9 | 6244560 |
| 10 | 83613600 |
| 11 | 1216131840 |
| 12 | 19084222080 |
| 13 | 321271030080 |
| 14 | 5773503415680 |
| 15 | 110288062684800 |
| 16 | 2231100039168000 |
| 17 | 47640952315756800 |
| 18 | 1070630750168179200 |
| 19 | 25255541547460224000 |
| 20 | 623884298434645248000 |
| 21 | 16104652019138319436800 |
[0,1,2,12,72,540,4680,46200,510720,6244560, 83613600,1216131840,19084222080,321271030080, 5773503415680,110288062684800,2231100039168000, 47640952315756800,1070630750168179200, 25255541547460224000,623884298434645248000, 16104652019138319436800] |