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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 16 |
| 4 | 88 |
| 5 | 632 |
| 6 | 5552 |
| 7 | 57824 |
| 8 | 695776 |
| 9 | 9500128 |
| 10 | 145097152 |
| 11 | 2451080192 |
| 12 | 45373649024 |
| 13 | 913400022656 |
| 14 | 19865889564928 |
| 15 | 464227147597312 |
| 16 | 11599471170191872 |
| 17 | 308605525316616704 |
| 18 | 8709955613991289856 |
| 19 | 259922447412719218688 |
| 20 | 8177253768239405504512 |
[1,2,4,16,88,632,5552,57824,695776,9500128, 145097152,2451080192,45373649024,913400022656, 19865889564928,464227147597312,11599471170191872, 308605525316616704,8709955613991289856, 259922447412719218688,8177253768239405504512] |