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| n | a(n) |
|---|---|
| 1 | 40 |
| 2 | 180 |
| 3 | 816 |
| 4 | 3728 |
| 5 | 17152 |
| 6 | 79424 |
| 7 | 369920 |
| 8 | 1731840 |
| 9 | 8144896 |
| 10 | 38458368 |
| 11 | 182218752 |
| 12 | 865931264 |
| 13 | 4125491200 |
| 14 | 19697254400 |
| 15 | 94217240576 |
| 16 | 451363012608 |
| 17 | 2165141143552 |
| 18 | 10397297147904 |
| 19 | 49974875258880 |
| 20 | 240389177999360 |
| 21 | 1157058166521856 |
[40,180,816,3728,17152,79424,369920,1731840, 8144896,38458368,182218752,865931264,4125491200, 19697254400,94217240576,451363012608, 2165141143552,10397297147904,49974875258880, 240389177999360,1157058166521856] |