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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 104 |
| 6 | 572 |
| 7 | 3708 |
| 8 | 26080 |
| 9 | 203656 |
| 10 | 1891158 |
| 11 | 17801198 |
| 12 | 187809048 |
| 13 | 2197262096 |
| 14 | 25480703902 |
| 15 | 331576359352 |
| 16 | 4786283287650 |
[1,2,6,24,104,572,3708,26080,203656,1891158, 17801198,187809048,2197262096,25480703902, 331576359352,4786283287650] |