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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | 8 |
| 4 | 20 |
| 5 | 55 |
| 6 | 160 |
| 7 | 493 |
| 8 | 1579 |
| 9 | 5212 |
| 10 | 17595 |
| 11 | 60462 |
| 12 | 210749 |
| 13 | 743284 |
| 14 | 2647461 |
| 15 | 9509504 |
[0,1,3,8,20,55,160,493,1579,5212,17595,60462, 210749,743284,2647461,9509504] |