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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 25 |
| 5 | 138 |
| 6 | 972 |
| 7 | 8477 |
| 8 | 89405 |
| 9 | 1119280 |
| 10 | 16384508 |
| 11 | 276961252 |
| 12 | 5349351298 |
| 13 | 116985744912 |
| 14 | 2873993336097 |
| 15 | 78768494976617 |
[1,2,6,25,138,972,8477,89405,1119280,16384508, 276961252,5349351298,116985744912,2873993336097, 78768494976617] |