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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 24 |
| 4 | 112 |
| 5 | 688 |
| 6 | 4032 |
| 7 | 25856 |
| 8 | 165888 |
| 9 | 1103616 |
| 10 | 7412480 |
| 11 | 50699776 |
| 12 | 350087168 |
| 13 | 2444208128 |
| 14 | 17198686208 |
| 15 | 121945948160 |
| 16 | 870026493952 |
| 17 | 6242802761728 |
| 18 | 45016506564608 |
| 19 | 326071359897600 |
| 20 | 2371312632397824 |
| 21 | 17307835567636480 |
| 22 | 126743329792327680 |
[1,2,4,24,112,688,4032,25856,165888,1103616, 7412480,50699776,350087168,2444208128,17198686208, 121945948160,870026493952,6242802761728, 45016506564608,326071359897600,2371312632397824, 17307835567636480,126743329792327680] |