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| n | a(n) |
|---|---|
| -1 | 1 |
| 0 | 4 |
| 1 | 17 |
| 2 | 136 |
| 3 | 1666 |
| 4 | 27200 |
| 5 | 555152 |
| 6 | 13596736 |
| 7 | 388512016 |
| 8 | 12687211520 |
| 9 | 466101423872 |
| 10 | 19026204891136 |
| 11 | 854312172054016 |
| 12 | 41847505957437440 |
| 13 | 2220673304780705792 |
| 14 | 126906669626284711936 |
| 15 | 7770472824437270972416 |
| 16 | 507503647885498965032960 |
| 17 | 35217605908746553266470912 |
[1,4,17,136,1666,27200,555152,13596736,388512016, 12687211520,466101423872,19026204891136, 854312172054016,41847505957437440, 2220673304780705792,126906669626284711936, 7770472824437270972416,507503647885498965032960, 35217605908746553266470912] |