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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 4 |
| 5 | 9 |
| 6 | 20 |
| 7 | 44 |
| 8 | 113 |
| 9 | 329 |
| 10 | 1044 |
| 11 | 3622 |
| 12 | 13544 |
| 13 | 53596 |
| 14 | 223084 |
| 15 | 969158 |
[0,0,2,4,9,20,44,113,329,1044,3622,13544,53596, 223084,969158] |