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| n | a(n) |
|---|---|
| 4 | 1 |
| 5 | 13 |
| 6 | 37 |
| 7 | 73 |
| 8 | 270 |
| 9 | 3023 |
| 10 | 31666 |
| 11 | 204526 |
| 12 | 1765714 |
| 13 | 30617532 |
| 14 | 748500437 |
| 15 | 15766186082 |
| 16 | 363909913887 |
| 17 | 12760152079877 |
| 18 | 642694450893529 |
[1,13,37,73,270,3023,31666,204526,1765714, 30617532,748500437,15766186082,363909913887, 12760152079877,642694450893529] |