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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 3 |
| 3 | 6 |
| 4 | 31 |
| 5 | 126 |
| 6 | 589 |
| 7 | 2772 |
| 8 | 13485 |
| 9 | 66780 |
| 10 | 336207 |
| 11 | 1714698 |
| 12 | 8841627 |
| 13 | 46015002 |
| 14 | 241394073 |
| 15 | 1275137448 |
| 16 | 6776728825 |
| 17 | 36208438488 |
| 18 | 194388488155 |
| 19 | 1048061471886 |
| 20 | 5672504958327 |
| 21 | 30808982057046 |
| 22 | 167864115588325 |
| 23 | 917271225518076 |
| 24 | 5025659929354981 |
[1,0,3,6,31,126,589,2772,13485,66780,336207, 1714698,8841627,46015002,241394073,1275137448, 6776728825,36208438488,194388488155,1048061471886, 5672504958327,30808982057046,167864115588325, 917271225518076,5025659929354981] |