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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 12 |
| 3 | 57 |
| 4 | 294 |
| 5 | 1578 |
| 6 | 8658 |
| 7 | 48177 |
| 8 | 270774 |
| 9 | 1533450 |
| 10 | 8736432 |
| 11 | 50016090 |
| 12 | 287497380 |
| 13 | 1658174352 |
| 14 | 9591422286 |
| 15 | 55618701057 |
| 16 | 323225066790 |
| 17 | 1882009941570 |
| 18 | 10976834700792 |
| 19 | 64119701075886 |
| 20 | 375057555388884 |
| 21 | 2196539772794172 |
| 22 | 12878508015774468 |
[1,3,12,57,294,1578,8658,48177,270774,1533450, 8736432,50016090,287497380,1658174352,9591422286, 55618701057,323225066790,1882009941570, 10976834700792,64119701075886,375057555388884, 2196539772794172,12878508015774468] |