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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 6 |
| 4 | 32 |
| 5 | 136 |
| 6 | 640 |
| 7 | 2593 |
| 8 | 11860 |
| 9 | 47532 |
| 10 | 215531 |
| 11 | 861334 |
| 12 | 3893621 |
| 13 | 15549166 |
| 14 | 70199065 |
| 15 | 280316029 |
| 16 | 1264697307 |
| 17 | 5050617474 |
| 18 | 22776900816 |
| 19 | 90972831448 |
| 20 | 410117333080 |
[1,6,32,136,640,2593,11860,47532,215531,861334, 3893621,15549166,70199065,280316029,1264697307, 5050617474,22776900816,90972831448,410117333080] |