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| n | a(n) |
|---|---|
| 0 | 2 |
| 1 | 9 |
| 2 | 56 |
| 3 | 378 |
| 4 | 2585 |
| 5 | 17712 |
| 6 | 121394 |
| 7 | 832041 |
| 8 | 5702888 |
| 9 | 39088170 |
| 10 | 267914297 |
| 11 | 1836311904 |
| 12 | 12586269026 |
| 13 | 86267571273 |
| 14 | 591286729880 |
| 15 | 4052739537882 |
| 16 | 27777890035289 |
| 17 | 190392490709136 |
| 18 | 1304969544928658 |
| 19 | 8944394323791465 |
| 20 | 61305790721611592 |
| 21 | 420196140727489674 |
[2,9,56,378,2585,17712,121394,832041,5702888, 39088170,267914297,1836311904,12586269026, 86267571273,591286729880,4052739537882, 27777890035289,190392490709136,1304969544928658, 8944394323791465,61305790721611592, 420196140727489674] |