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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 9 |
| 5 | 30 |
| 6 | 136 |
| 7 | 882 |
| 8 | 7626 |
| 9 | 84448 |
| 10 | 1159912 |
| 11 | 19226112 |
| 12 | 376464500 |
| 13 | 8556370952 |
| 14 | 222510227460 |
| 15 | 6542050923204 |
| 16 | 215278202878118 |
| 17 | 7860760142260830 |
| 18 | 316135809596510856 |
[1,1,4,9,30,136,882,7626,84448,1159912,19226112, 376464500,8556370952,222510227460,6542050923204, 215278202878118,7860760142260830, 316135809596510856] |