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| n | a(n) |
|---|---|
| 1 | 4 |
| 2 | 18 |
| 3 | 78 |
| 4 | 331 |
| 5 | 1400 |
| 6 | 5949 |
| 7 | 25277 |
| 8 | 107353 |
| 9 | 455938 |
| 10 | 1936500 |
| 11 | 8224877 |
| 12 | 34933256 |
| 13 | 148370893 |
| 14 | 630171269 |
| 15 | 2676507659 |
| 16 | 11367850562 |
| 17 | 48282330086 |
| 18 | 205068091043 |
| 19 | 870979546682 |
| 20 | 3699285278069 |
| 21 | 15711863292777 |
| 22 | 66732525229601 |
[4,18,78,331,1400,5949,25277,107353,455938, 1936500,8224877,34933256,148370893,630171269, 2676507659,11367850562,48282330086,205068091043, 870979546682,3699285278069,15711863292777, 66732525229601] |