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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 0 |
| 4 | 1 |
| 5 | 2 |
| 6 | 7 |
| 7 | 27 |
| 8 | 126 |
| 9 | 664 |
| 10 | 3954 |
| 11 | 26190 |
| 12 | 190754 |
| 13 | 1514332 |
| 14 | 12998035 |
| 15 | 119803771 |
| 16 | 1178740932 |
| 17 | 12316480222 |
| 18 | 136060611189 |
| 19 | 1582930919092 |
| 20 | 19328253734491 |
[1,1,1,0,1,2,7,27,126,664,3954,26190,190754, 1514332,12998035,119803771,1178740932,12316480222, 136060611189,1582930919092,19328253734491] |