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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 0 |
| 4 | 0 |
| 5 | 2 |
| 6 | 4 |
| 7 | 10 |
| 8 | 36 |
| 9 | 126 |
| 10 | 454 |
| 11 | 1744 |
| 12 | 6892 |
| 13 | 28486 |
| 14 | 120962 |
| 15 | 531660 |
| 16 | 2398248 |
| 17 | 11127674 |
| 18 | 52888998 |
| 19 | 257570104 |
| 20 | 1282439216 |
[1,1,2,0,0,2,4,10,36,126,454,1744,6892,28486, 120962,531660,2398248,11127674,52888998,257570104, 1282439216] |