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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 18 |
| 4 | 216 |
| 5 | 4360 |
| 6 | 125040 |
| 7 | 4757424 |
| 8 | 233179520 |
| 9 | 14258991744 |
| 10 | 1060121721600 |
| 11 | 94009965280000 |
| 12 | 9789344262601728 |
| 13 | 1181209592291349504 |
| 14 | 163306868988824078336 |
| 15 | 25621879112031299758080 |
| 16 | 4524060645635205169643520 |
| 17 | 892453349895680565864595456 |
| 18 | 195425578879660458241000538112 |
[1,1,2,18,216,4360,125040,4757424,233179520, 14258991744,1060121721600,94009965280000, 9789344262601728,1181209592291349504, 163306868988824078336,25621879112031299758080, 4524060645635205169643520, 892453349895680565864595456, 195425578879660458241000538112] |