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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 16 |
| 4 | 114 |
| 5 | 644 |
| 6 | 3270 |
| 7 | 15642 |
| 8 | 72072 |
| 9 | 323752 |
| 10 | 1428102 |
| 11 | 6214520 |
| 12 | 26761196 |
| 13 | 114287736 |
| 14 | 484816540 |
| 15 | 2045277990 |
| 16 | 8588492100 |
| 17 | 35923392720 |
| 18 | 149753379270 |
| 19 | 622458753840 |
| 20 | 2580709189740 |
| 21 | 10675646755800 |
| 22 | 44074384410420 |
[1,16,114,644,3270,15642,72072,323752,1428102, 6214520,26761196,114287736,484816540,2045277990, 8588492100,35923392720,149753379270,622458753840, 2580709189740,10675646755800,44074384410420] |