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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 4 |
| 5 | 13 |
| 6 | 42 |
| 7 | 139 |
| 8 | 470 |
| 9 | 1616 |
| 10 | 5632 |
| 11 | 19852 |
| 12 | 70654 |
| 13 | 253559 |
| 14 | 916558 |
| 15 | 3334211 |
| 16 | 12197142 |
| 17 | 44842184 |
| 18 | 165597008 |
| 19 | 613991206 |
| 20 | 2284809072 |
| 21 | 8530458154 |
| 22 | 31945128628 |
| 23 | 119960276246 |
| 24 | 451621453764 |
| 25 | 1704240175868 |
| 26 | 6445111657272 |
[1,0,0,1,4,13,42,139,470,1616,5632,19852,70654, 253559,916558,3334211,12197142,44842184,165597008, 613991206,2284809072,8530458154,31945128628, 119960276246,451621453764,1704240175868, 6445111657272] |