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| n | a(n) |
|---|---|
| 4 | 1 |
| 5 | 4 |
| 6 | 13 |
| 7 | 28 |
| 8 | 49 |
| 9 | 171 |
| 10 | 1310 |
| 11 | 8460 |
| 12 | 42491 |
| 13 | 242978 |
| 14 | 2107793 |
| 15 | 27648766 |
| 16 | 373047925 |
| 17 | 4984501036 |
| 18 | 77677934468 |
| 19 | 1580716536075 |
| 20 | 41780194476260 |
[1,4,13,28,49,171,1310,8460,42491,242978,2107793, 27648766,373047925,4984501036,77677934468, 1580716536075,41780194476260] |