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| n | a(n) |
|---|---|
| 6 | 1 |
| 7 | 4 |
| 8 | 10 |
| 9 | 19 |
| 10 | 51 |
| 11 | 170 |
| 12 | 491 |
| 13 | 1673 |
| 14 | 7735 |
| 15 | 36917 |
| 16 | 181725 |
| 17 | 1063340 |
| 18 | 7115095 |
| 19 | 51066154 |
| 20 | 415590144 |
| 21 | 3918376915 |
[1,4,10,19,51,170,491,1673,7735,36917,181725, 1063340,7115095,51066154,415590144,3918376915] |