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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 108 |
| 5 | 1208 |
| 6 | 15536 |
| 7 | 220832 |
| 8 | 3390480 |
| 9 | 55411872 |
| 10 | 954553664 |
| 11 | 17211258240 |
| 12 | 323148560768 |
| 13 | 6293245904640 |
| 14 | 126740607526400 |
| 15 | 2633207863038976 |
| 16 | 56330595706808576 |
| 17 | 1238815010325576192 |
| 18 | 27970477203200824320 |
[1,2,12,108,1208,15536,220832,3390480,55411872, 954553664,17211258240,323148560768,6293245904640, 126740607526400,2633207863038976, 56330595706808576,1238815010325576192, 27970477203200824320] |