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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 9 |
| 4 | 48 |
| 5 | 315 |
| 6 | 2496 |
| 7 | 22491 |
| 8 | 223728 |
| 9 | 2437371 |
| 10 | 28931040 |
| 11 | 371291283 |
| 12 | 5111412120 |
| 13 | 75014135235 |
| 14 | 1168157451384 |
| 15 | 19228202401635 |
| 16 | 333378840718944 |
| 17 | 6069073767712587 |
| 18 | 115683487658404272 |
| 19 | 2303091818149762899 |
| 20 | 47784447190060311240 |
| 21 | 1031179733234906055507 |
[1,0,2,9,48,315,2496,22491,223728,2437371, 28931040,371291283,5111412120,75014135235, 1168157451384,19228202401635,333378840718944, 6069073767712587,115683487658404272, 2303091818149762899,47784447190060311240, 1031179733234906055507] |