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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 10 |
| 5 | 46 |
| 6 | 244 |
| 7 | 1481 |
| 8 | 10020 |
| 9 | 74400 |
| 10 | 599573 |
| 11 | 5200284 |
| 12 | 48223360 |
| 13 | 475557054 |
| 14 | 4965035754 |
| 15 | 54672110310 |
| 16 | 632853655686 |
| 17 | 7678552433184 |
| 18 | 97404631390960 |
| 19 | 1288861146261679 |
| 20 | 17752479062092470 |
| 21 | 254051633672160696 |
[1,1,1,3,10,46,244,1481,10020,74400,599573, 5200284,48223360,475557054,4965035754,54672110310, 632853655686,7678552433184,97404631390960, 1288861146261679,17752479062092470, 254051633672160696] |