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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 720 |
| 7 | 4768 |
| 8 | 35968 |
| 9 | 312064 |
| 10 | 3004160 |
| 11 | 31764480 |
| 12 | 365798400 |
| 13 | 4555499520 |
| 14 | 61232590848 |
| 15 | 882227765248 |
| 16 | 13547017240576 |
| 17 | 221038858829824 |
| 18 | 3818608204709888 |
| 19 | 69637156745773056 |
| 20 | 1336921845773107200 |
| 21 | 26947721453843251200 |
| 22 | 569023211226594803712 |
[1,1,2,6,24,120,720,4768,35968,312064,3004160, 31764480,365798400,4555499520,61232590848, 882227765248,13547017240576,221038858829824, 3818608204709888,69637156745773056, 1336921845773107200,26947721453843251200, 569023211226594803712] |