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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 18 |
| 3 | 144 |
| 4 | 1584 |
| 5 | 22176 |
| 6 | 354816 |
| 7 | 6741504 |
| 8 | 141571584 |
| 9 | 3397718016 |
| 10 | 91738386432 |
| 11 | 2660413206528 |
| 12 | 85133222608896 |
| 13 | 2979662791311360 |
| 14 | 110247523278520320 |
| 15 | 4409900931140812800 |
| 16 | 185215839107914137600 |
| 17 | 8334712759856136192000 |
| 18 | 400066212473094537216000 |
[1,3,18,144,1584,22176,354816,6741504,141571584, 3397718016,91738386432,2660413206528, 85133222608896,2979662791311360, 110247523278520320,4409900931140812800, 185215839107914137600,8334712759856136192000, 400066212473094537216000] |