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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 7 |
| 5 | 25 |
| 6 | 102 |
| 7 | 456 |
| 8 | 2219 |
| 9 | 11640 |
| 10 | 65364 |
| 11 | 390646 |
| 12 | 2472719 |
| 13 | 16508791 |
| 14 | 115839661 |
| 15 | 851634863 |
| 16 | 6542134884 |
| 17 | 52384882759 |
| 18 | 436290809772 |
| 19 | 3772143122161 |
| 20 | 33797290492507 |
| 21 | 313304547351868 |
| 22 | 3000631062271288 |
| 23 | 29651208549845055 |
[0,1,2,7,25,102,456,2219,11640,65364,390646, 2472719,16508791,115839661,851634863,6542134884, 52384882759,436290809772,3772143122161, 33797290492507,313304547351868,3000631062271288, 29651208549845055] |