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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 1 |
| 3 | 9 |
| 4 | 39 |
| 5 | 150 |
| 6 | 1365 |
| 7 | 13545 |
| 8 | 105945 |
| 9 | 918540 |
| 10 | 10603845 |
| 11 | 127806525 |
| 12 | 1468823895 |
| 13 | 18253765530 |
| 14 | 257397445305 |
| 15 | 3770163121725 |
| 16 | 55637459903025 |
| 17 | 866703333295800 |
| 18 | 14468243658093225 |
| 19 | 250223925107581425 |
| 20 | 4426399346291497575 |
| 21 | 81488489549760042750 |
[1,0,1,9,39,150,1365,13545,105945,918540,10603845, 127806525,1468823895,18253765530,257397445305, 3770163121725,55637459903025,866703333295800, 14468243658093225,250223925107581425, 4426399346291497575,81488489549760042750] |