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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 8 |
| 4 | 48 |
| 5 | 258 |
| 6 | 1518 |
| 7 | 8910 |
| 8 | 53526 |
| 9 | 323796 |
| 10 | 1976876 |
| 11 | 12138456 |
| 12 | 74921904 |
| 13 | 464320368 |
| 14 | 2887660168 |
| 15 | 18011618368 |
| 16 | 112633305568 |
| 17 | 705899650498 |
| 18 | 4432668783838 |
| 19 | 27882818399038 |
| 20 | 175661366346838 |
| 21 | 1108193133814138 |
| 22 | 6999963827434378 |
| 23 | 44265660573879298 |
[0,2,8,48,258,1518,8910,53526,323796,1976876, 12138456,74921904,464320368,2887660168, 18011618368,112633305568,705899650498, 4432668783838,27882818399038,175661366346838, 1108193133814138,6999963827434378, 44265660573879298] |