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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 3 |
| 5 | 13 |
| 6 | 67 |
| 7 | 425 |
| 8 | 3103 |
| 9 | 25751 |
| 10 | 239483 |
| 11 | 2466678 |
| 12 | 27873456 |
| 13 | 342843514 |
| 14 | 4559818741 |
| 15 | 65205407995 |
| 16 | 997642742322 |
| 17 | 16261576699844 |
| 18 | 281325276907304 |
| 19 | 5148252567403659 |
| 20 | 99361274550890613 |
| 21 | 2017033873383079454 |
[1,0,0,1,3,13,67,425,3103,25751,239483,2466678, 27873456,342843514,4559818741,65205407995, 997642742322,16261576699844,281325276907304, 5148252567403659,99361274550890613, 2017033873383079454] |