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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 8 |
| 3 | 50 |
| 4 | 422 |
| 5 | 4480 |
| 6 | 57300 |
| 7 | 857364 |
| 8 | 14690244 |
| 9 | 283594200 |
| 10 | 6090223440 |
| 11 | 144002872968 |
| 12 | 3717346949880 |
| 13 | 104024775376416 |
| 14 | 3136618299654000 |
| 15 | 101380000924630416 |
| 16 | 3496607473494821136 |
| 17 | 128180947344040558752 |
| 18 | 4976894571781037789184 |
| 19 | 204030008190766804890912 |
| 20 | 8806691099474138713650528 |
[1,2,8,50,422,4480,57300,857364,14690244, 283594200,6090223440,144002872968,3717346949880, 104024775376416,3136618299654000, 101380000924630416,3496607473494821136, 128180947344040558752,4976894571781037789184, 204030008190766804890912, 8806691099474138713650528] |