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| n | a(n) |
|---|---|
| 4 | 1 |
| 5 | 7 |
| 6 | 25 |
| 7 | 55 |
| 8 | 97 |
| 9 | 706 |
| 10 | 9275 |
| 11 | 70904 |
| 12 | 406991 |
| 13 | 3864451 |
| 14 | 77404600 |
| 15 | 1807280192 |
| 16 | 33936037037 |
| 17 | 736180071815 |
| 18 | 24815800630395 |
[1,7,25,55,97,706,9275,70904,406991,3864451, 77404600,1807280192,33936037037,736180071815, 24815800630395] |