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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 15 |
| 2 | 154 |
| 3 | 1350 |
| 4 | 10891 |
| 5 | 83685 |
| 6 | 623764 |
| 7 | 4558380 |
| 8 | 32875381 |
| 9 | 234980955 |
| 10 | 1669192174 |
| 11 | 11806149810 |
| 12 | 83252603071 |
| 13 | 585817587825 |
| 14 | 4115974729384 |
| 15 | 28888095527640 |
| 16 | 202598073849961 |
| 17 | 1420093671872295 |
| 18 | 9950191865139394 |
[1,15,154,1350,10891,83685,623764,4558380, 32875381,234980955,1669192174,11806149810, 83252603071,585817587825,4115974729384, 28888095527640,202598073849961,1420093671872295, 9950191865139394] |