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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | 11 |
| 4 | 25 |
| 5 | 137 |
| 6 | 294 |
| 7 | 2178 |
| 8 | 4566 |
| 9 | 42774 |
| 10 | 88572 |
| 11 | 1004532 |
| 12 | 2064504 |
| 13 | 27503832 |
| 14 | 56243184 |
| 15 | 860945040 |
| 16 | 1754322480 |
| 17 | 30342400560 |
| 18 | 61664980320 |
| 19 | 1189277851680 |
| 20 | 2412077832000 |
| 21 | 51324077044800 |
| 22 | 103928089910400 |
| 23 | 2418504655996800 |
[0,1,3,11,25,137,294,2178,4566,42774,88572, 1004532,2064504,27503832,56243184,860945040, 1754322480,30342400560,61664980320,1189277851680, 2412077832000,51324077044800,103928089910400, 2418504655996800] |