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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 2 |
| 6 | 3 |
| 7 | 6 |
| 8 | 8 |
| 9 | 21 |
| 10 | 54 |
| 11 | 176 |
| 12 | 1155 |
| 13 | 9558 |
| 14 | 203456 |
| 15 | 11040645 |
| 16 | 1944642006 |
| 17 | 2246285672576 |
| 18 | 21470102051374515 |
| 19 | 4368221476369196469462 |
| 20 | 48227982626747161978326473216 |
| 21 | 93786160880652497618461924784373935445 |
[1,1,1,2,2,3,6,8,21,54,176,1155,9558,203456, 11040645,1944642006,2246285672576, 21470102051374515,4368221476369196469462, 48227982626747161978326473216, 93786160880652497618461924784373935445] |