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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 38 |
| 3 | 252 |
| 4 | 1740 |
| 5 | 12456 |
| 6 | 92136 |
| 7 | 702288 |
| 8 | 5503632 |
| 9 | 44258400 |
| 10 | 364615776 |
| 11 | 3072862656 |
| 12 | 26458723008 |
| 13 | 232501041792 |
| 14 | 2082933048960 |
| 15 | 19007627463936 |
| 16 | 176533756252416 |
| 17 | 1667446616360448 |
| 18 | 16006827410744832 |
| 19 | 156069042653445120 |
[1,6,38,252,1740,12456,92136,702288,5503632, 44258400,364615776,3072862656,26458723008, 232501041792,2082933048960,19007627463936, 176533756252416,1667446616360448, 16006827410744832,156069042653445120] |