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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 5 |
| 3 | 18 |
| 4 | 88 |
| 5 | 489 |
| 6 | 3071 |
| 7 | 20667 |
| 8 | 146381 |
| 9 | 1072760 |
| 10 | 8071728 |
| 11 | 61990477 |
| 12 | 484182622 |
| 13 | 3835654678 |
| 14 | 30757242535 |
| 15 | 249255692801 |
| 16 | 2038827903834 |
| 17 | 16815060576958 |
| 18 | 139706974995635 |
| 19 | 1168468902294726 |
| 20 | 9831504782276593 |
| 21 | 83174244225508659 |
| 22 | 707159273362126228 |
| 23 | 6039827641569969225 |
[1,2,5,18,88,489,3071,20667,146381,1072760, 8071728,61990477,484182622,3835654678,30757242535, 249255692801,2038827903834,16815060576958, 139706974995635,1168468902294726,9831504782276593, 83174244225508659,707159273362126228, 6039827641569969225] |