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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 13 |
| 4 | 69 |
| 5 | 419 |
| 6 | 2809 |
| 7 | 20353 |
| 8 | 157199 |
| 9 | 1281993 |
| 10 | 10963825 |
| 11 | 97828031 |
| 12 | 907177801 |
| 13 | 8716049417 |
| 14 | 86553001779 |
| 15 | 886573220093 |
| 16 | 9351927111901 |
| 17 | 101447092428243 |
| 18 | 1130357986741545 |
| 19 | 12923637003161409 |
| 20 | 151479552582252239 |
[1,1,3,13,69,419,2809,20353,157199,1281993, 10963825,97828031,907177801,8716049417, 86553001779,886573220093,9351927111901, 101447092428243,1130357986741545, 12923637003161409,151479552582252239] |