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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 18 |
| 3 | 144 |
| 4 | 432 |
| 5 | 5400 |
| 6 | 23328 |
| 7 | 254016 |
| 8 | 829440 |
| 9 | 12607488 |
| 10 | 53460000 |
| 11 | 633048768 |
| 12 | 2176782336 |
| 13 | 35784141120 |
| 14 | 173408594688 |
| 15 | 1903214880000 |
| 16 | 6849130659840 |
| 17 | 112370402481120 |
| 18 | 534356527841280 |
| 19 | 6501218491422144 |
| 20 | 20323353600000000 |
| 21 | 367285791437881344 |
| 22 | 1782862092373874688 |
[1,6,18,144,432,5400,23328,254016,829440,12607488, 53460000,633048768,2176782336,35784141120, 173408594688,1903214880000,6849130659840, 112370402481120,534356527841280,6501218491422144, 20323353600000000,367285791437881344, 1782862092373874688] |