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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 17 |
| 5 | 126 |
| 6 | 832 |
| 7 | 8646 |
| 8 | 83281 |
| 9 | 1035670 |
| 10 | 13155686 |
| 11 | 200866326 |
| 12 | 3090454952 |
| 13 | 55704133590 |
| 14 | 1028017657682 |
| 15 | 21123701763534 |
| 16 | 453986750729681 |
| 17 | 10610386574074710 |
| 18 | 258237311112260158 |
[1,1,4,17,126,832,8646,83281,1035670,13155686, 200866326,3090454952,55704133590,1028017657682, 21123701763534,453986750729681,10610386574074710, 258237311112260158] |