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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 24 |
| 3 | 96 |
| 4 | 624 |
| 5 | 2496 |
| 6 | 14976 |
| 7 | 59904 |
| 8 | 390624 |
| 9 | 1562496 |
| 10 | 9374976 |
| 11 | 37499904 |
| 12 | 243749376 |
| 13 | 974997504 |
| 14 | 5849985024 |
| 15 | 23399940096 |
| 16 | 152587890624 |
| 17 | 610351562496 |
| 18 | 3662109374976 |
| 19 | 14648437499904 |
| 20 | 95214843749376 |
| 21 | 380859374997504 |
[1,4,24,96,624,2496,14976,59904,390624,1562496, 9374976,37499904,243749376,974997504,5849985024, 23399940096,152587890624,610351562496, 3662109374976,14648437499904,95214843749376, 380859374997504] |