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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 36 |
| 4 | 416 |
| 5 | 140 |
| 6 | 4940 |
| 7 | 250160 |
| 8 | 160940 |
| 9 | 936464640 |
| 10 | 9364646400 |
| 11 | 981811366400 |
| 12 | 1649810013600 |
| 13 | 3644490406400 |
| 14 | 6449149644811400 |
| 15 | 1904936491693664000 |
| 16 | 408144496481646464000 |
| 17 | 925253664491646408136000 |
| 18 | 36160494994902549464000 |
| 19 | 141361625100160646494000 |
[1,4,36,416,140,4940,250160,160940,936464640, 9364646400,981811366400,1649810013600, 3644490406400,6449149644811400, 1904936491693664000,408144496481646464000, 925253664491646408136000,36160494994902549464000, 141361625100160646494000] |