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| n | a(n) |
|---|---|
| 1 | 6 |
| 2 | 40 |
| 3 | 308 |
| 4 | 2260 |
| 5 | 16812 |
| 6 | 124644 |
| 7 | 924900 |
| 8 | 6862052 |
| 9 | 50913012 |
| 10 | 377747700 |
| 11 | 2802692276 |
| 12 | 20794524084 |
| 13 | 154284599124 |
| 14 | 1144711823796 |
| 15 | 8493168927828 |
| 16 | 63014915159220 |
| 17 | 467538037568404 |
| 18 | 3468890119531892 |
| 19 | 25737368287958996 |
| 20 | 190957944347003188 |
[6,40,308,2260,16812,124644,924900,6862052, 50913012,377747700,2802692276,20794524084, 154284599124,1144711823796,8493168927828, 63014915159220,467538037568404,3468890119531892, 25737368287958996,190957944347003188] |