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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 16 |
| 4 | 85 |
| 5 | 481 |
| 6 | 3352 |
| 7 | 25420 |
| 8 | 223393 |
| 9 | 2157565 |
| 10 | 23241244 |
| 11 | 272933680 |
| 12 | 3496821133 |
| 13 | 48307202761 |
| 14 | 717473918560 |
| 15 | 11381186498836 |
| 16 | 192155770419673 |
| 17 | 3438337498017781 |
| 18 | 65004294514876996 |
| 19 | 1294456866053992600 |
| 20 | 27081588485949257605 |
[1,4,16,85,481,3352,25420,223393,2157565,23241244, 272933680,3496821133,48307202761,717473918560, 11381186498836,192155770419673,3438337498017781, 65004294514876996,1294456866053992600, 27081588485949257605] |