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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 3 |
| 3 | 21 |
| 4 | 163 |
| 5 | 1259 |
| 6 | 9657 |
| 7 | 73949 |
| 8 | 566797 |
| 9 | 4352755 |
| 10 | 33501979 |
| 11 | 258431853 |
| 12 | 1997743677 |
| 13 | 15473296249 |
[1,3,21,163,1259,9657,73949,566797,4352755, 33501979,258431853,1997743677,15473296249] |