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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 21 |
| 3 | 63 |
| 4 | 987 |
| 5 | 2961 |
| 6 | 20727 |
| 7 | 62181 |
| 8 | 2178309 |
| 9 | 6534927 |
| 10 | 45744489 |
| 11 | 137233467 |
| 12 | 2149990983 |
| 13 | 6449972949 |
| 14 | 45149810643 |
| 15 | 135449431929 |
| 16 | 10610209857723 |
| 17 | 31830629573169 |
| 18 | 222814407012183 |
| 19 | 668443221036549 |
| 20 | 10472277129572601 |
[1,3,21,63,987,2961,20727,62181,2178309,6534927, 45744489,137233467,2149990983,6449972949, 45149810643,135449431929,10610209857723, 31830629573169,222814407012183,668443221036549, 10472277129572601] |