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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 10 |
| 6 | 4 |
| 7 | 12 |
| 8 | 32 |
| 9 | 96 |
| 10 | 144 |
| 11 | 528 |
| 12 | 1712 |
| 13 | 7472 |
| 14 | 24500 |
| 15 | 103536 |
| 16 | 486020 |
| 17 | 2218808 |
| 18 | 11113020 |
| 19 | 59242576 |
| 20 | 342584556 |
| 21 | 1981826412 |
[1,0,0,2,10,4,12,32,96,144,528,1712,7472,24500, 103536,486020,2218808,11113020,59242576,342584556, 1981826412] |