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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 6 |
| 3 | 18 |
| 4 | 45 |
| 5 | 135 |
| 6 | 378 |
| 7 | 1134 |
| 8 | 3321 |
| 9 | 9963 |
| 10 | 29646 |
| 11 | 88938 |
| 12 | 266085 |
| 13 | 798255 |
| 14 | 2392578 |
| 15 | 7177734 |
| 16 | 21526641 |
| 17 | 64579923 |
| 18 | 193720086 |
| 19 | 581160258 |
| 20 | 1743421725 |
| 21 | 5230265175 |
| 22 | 15690618378 |
| 23 | 47071855134 |
| 24 | 141215033961 |
| 25 | 423645101883 |
[1,3,6,18,45,135,378,1134,3321,9963,29646,88938, 266085,798255,2392578,7177734,21526641,64579923, 193720086,581160258,1743421725,5230265175, 15690618378,47071855134,141215033961,423645101883] |