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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 13 |
| 5 | 67 |
| 6 | 305 |
| 7 | 2359 |
| 8 | 16495 |
| 9 | 141643 |
| 10 | 1273691 |
| 11 | 15580299 |
| 12 | 152788607 |
| 13 | 2206382433 |
| 14 | 28916044241 |
| 15 | 399450183613 |
[1,1,1,3,13,67,305,2359,16495,141643,1273691, 15580299,152788607,2206382433,28916044241, 399450183613] |