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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 5 |
| 4 | 21 |
| 5 | 114 |
| 6 | 780 |
| 7 | 6390 |
| 8 | 61110 |
| 9 | 667800 |
| 10 | 8210160 |
| 11 | 112152600 |
| 12 | 1685237400 |
| 13 | 27624920400 |
| 14 | 490572482400 |
| 15 | 9381882510000 |
| 16 | 192238348302000 |
| 17 | 4201639474032000 |
| 18 | 97572286427616000 |
| 19 | 2399151995223984000 |
| 20 | 62268748888378032000 |
| 21 | 1701213856860117600000 |
[1,2,5,21,114,780,6390,61110,667800,8210160, 112152600,1685237400,27624920400,490572482400, 9381882510000,192238348302000,4201639474032000, 97572286427616000,2399151995223984000, 62268748888378032000,1701213856860117600000] |