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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 21 |
| 4 | 504 |
| 5 | 21380 |
| 6 | 1405800 |
| 7 | 132139140 |
| 8 | 16801276800 |
| 9 | 2775758497344 |
| 10 | 577868994460800 |
| 11 | 147973478687496000 |
| 12 | 45703277816543424000 |
| 13 | 16753246307626306832640 |
| 14 | 7190163806348621417679360 |
| 15 | 3571395525388698501285792000 |
[1,2,21,504,21380,1405800,132139140,16801276800, 2775758497344,577868994460800,147973478687496000, 45703277816543424000,16753246307626306832640, 7190163806348621417679360, 3571395525388698501285792000] |