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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 4 |
| 3 | 28 |
| 4 | 108 |
| 5 | 2 |
| 6 | 13968 |
| 7 | 480 |
| 8 | 7914054 |
| 9 | 433284 |
| 10 | 18726123500 |
| 11 | 256 |
| 12 | 178290006448984 |
| 13 | 14454384 |
| 14 | 6631290958957860856 |
| 15 | 1401615406696 |
| 16 | 941558205279187913101914 |
| 17 | 1767136 |
| 18 | 500995759754153499284692617816 |
| 19 | 31163356068736 |
| 20 | 984452644453618816989710782436259368 |
[2,4,28,108,2,13968,480,7914054,433284, 18726123500,256,178290006448984,14454384, 6631290958957860856,1401615406696, 941558205279187913101914,1767136, 500995759754153499284692617816,31163356068736, 984452644453618816989710782436259368] |