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| n | a(n) |
|---|---|
| 1 | 18 |
| 2 | 200 |
| 3 | 1648 |
| 4 | 13732 |
| 5 | 106362 |
| 6 | 744564 |
| 7 | 4808120 |
| 8 | 29723864 |
| 9 | 180290280 |
| 10 | 1085927844 |
| 11 | 6524507992 |
| 12 | 39167586296 |
| 13 | 235053968050 |
| 14 | 1410450413584 |
| 15 | 8463032114236 |
| 16 | 50779132943420 |
[18,200,1648,13732,106362,744564,4808120,29723864, 180290280,1085927844,6524507992,39167586296, 235053968050,1410450413584,8463032114236, 50779132943420] |