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| n | a(n) |
|---|---|
| 1 | 81 |
| 2 | 360 |
| 3 | 1616 |
| 4 | 7016 |
| 5 | 31616 |
| 6 | 138988 |
| 7 | 620552 |
| 8 | 2734804 |
| 9 | 12176064 |
| 10 | 53818764 |
| 11 | 239177944 |
| 12 | 1058421796 |
| 13 | 4698785664 |
| 14 | 20810853180 |
| 15 | 92335672184 |
| 16 | 409124696372 |
| 17 | 1814626300736 |
| 18 | 8042404490476 |
| 19 | 35664530623384 |
| 20 | 158086995532676 |
[81,360,1616,7016,31616,138988,620552,2734804, 12176064,53818764,239177944,1058421796,4698785664, 20810853180,92335672184,409124696372, 1814626300736,8042404490476,35664530623384, 158086995532676] |