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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 12 |
| 3 | 40 |
| 4 | 144 |
| 5 | 550 |
| 6 | 1896 |
| 7 | 7584 |
| 8 | 27328 |
| 9 | 105348 |
| 10 | 398760 |
| 11 | 1538696 |
| 12 | 5872800 |
| 13 | 22646862 |
| 14 | 87492676 |
| 15 | 339055650 |
| 16 | 1313842904 |
| 17 | 5104724558 |
| 18 | 19873572892 |
| 19 | 77470783406 |
| 20 | 302258087616 |
| 21 | 1180840902336 |
| 22 | 4618922848536 |
| 23 | 18083348822516 |
| 24 | 70852652846320 |
[2,12,40,144,550,1896,7584,27328,105348,398760, 1538696,5872800,22646862,87492676,339055650, 1313842904,5104724558,19873572892,77470783406, 302258087616,1180840902336,4618922848536, 18083348822516,70852652846320] |