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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
| 5 | 2 |
| 6 | 6 |
| 7 | 27 |
| 8 | 177 |
| 9 | 1680 |
| 10 | 23009 |
| 11 | 455368 |
| 12 | 13067353 |
| 13 | 546378617 |
| 14 | 33472296082 |
| 15 | 3021920660821 |
| 16 | 404374532614122 |
| 17 | 80646410554881100 |
| 18 | 24095492607316134304 |
| 19 | 10837141045948365696938 |
| 20 | 7369252748590790186483284 |
| 21 | 7606603491185739308318700818 |
[1,1,1,2,6,27,177,1680,23009,455368,13067353, 546378617,33472296082,3021920660821, 404374532614122,80646410554881100, 24095492607316134304,10837141045948365696938, 7369252748590790186483284, 7606603491185739308318700818] |