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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 5 |
| 3 | 15 |
| 4 | 61 |
| 5 | 305 |
| 6 | 1830 |
| 7 | 12816 |
| 8 | 102532 |
| 9 | 922793 |
| 10 | 9227935 |
| 11 | 101507290 |
| 12 | 1218087483 |
| 13 | 15835137282 |
| 14 | 221691921954 |
| 15 | 3325378829312 |
| 16 | 53206061268999 |
| 17 | 904503041572984 |
| 18 | 16281054748313715 |
| 19 | 309340040217960589 |
| 20 | 6186800804359211794 |
[2,5,15,61,305,1830,12816,102532,922793,9227935, 101507290,1218087483,15835137282,221691921954, 3325378829312,53206061268999,904503041572984, 16281054748313715,309340040217960589, 6186800804359211794] |