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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 18 |
| 2 | 306 |
| 3 | 5049 |
| 4 | 83232 |
| 5 | 1370880 |
| 6 | 22579128 |
| 7 | 371880576 |
| 8 | 6124915584 |
| 9 | 100877977152 |
| 10 | 1661470525440 |
| 11 | 27364587522048 |
| 12 | 450697523867136 |
| 13 | 7423033790767104 |
| 14 | 122258117131149312 |
| 15 | 2013603551504732160 |
| 16 | 33164254102629777408 |
[1,18,306,5049,83232,1370880,22579128,371880576, 6124915584,100877977152,1661470525440, 27364587522048,450697523867136,7423033790767104, 122258117131149312,2013603551504732160, 33164254102629777408] |