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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 7 |
| 2 | 54 |
| 3 | 376 |
| 4 | 2583 |
| 5 | 17710 |
| 6 | 121392 |
| 7 | 832039 |
| 8 | 5702886 |
| 9 | 39088168 |
| 10 | 267914295 |
| 11 | 1836311902 |
| 12 | 12586269024 |
| 13 | 86267571271 |
| 14 | 591286729878 |
| 15 | 4052739537880 |
| 16 | 27777890035287 |
| 17 | 190392490709134 |
| 18 | 1304969544928656 |
| 19 | 8944394323791463 |
| 20 | 61305790721611590 |
| 21 | 420196140727489672 |
[0,7,54,376,2583,17710,121392,832039,5702886, 39088168,267914295,1836311902,12586269024, 86267571271,591286729878,4052739537880, 27777890035287,190392490709134,1304969544928656, 8944394323791463,61305790721611590, 420196140727489672] |