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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 10 |
| 4 | 75 |
| 5 | 450 |
| 6 | 2814 |
| 7 | 15202 |
| 8 | 89623 |
| 9 | 466252 |
| 10 | 2677281 |
| 11 | 13691160 |
| 12 | 77546684 |
| 13 | 393047294 |
| 14 | 2209036094 |
| 15 | 11140807218 |
| 16 | 62325916869 |
| 17 | 313402240000 |
| 18 | 1748294223916 |
| 19 | 8775335427968 |
| 20 | 48864101440273 |
| 21 | 244988564184682 |
| 22 | 1362584143931457 |
[1,10,75,450,2814,15202,89623,466252,2677281, 13691160,77546684,393047294,2209036094, 11140807218,62325916869,313402240000, 1748294223916,8775335427968,48864101440273, 244988564184682,1362584143931457] |