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| n | a(n) |
|---|---|
| 1 | 6 |
| 2 | 18 |
| 3 | 72 |
| 4 | 324 |
| 5 | 1555 |
| 6 | 7776 |
| 7 | 39990 |
| 8 | 209952 |
| 9 | 1119744 |
| 10 | 6046617 |
| 11 | 32981550 |
| 12 | 181398528 |
| 13 | 1004668770 |
| 14 | 5597440292 |
| 15 | 31345665638 |
| 16 | 176319369216 |
| 17 | 995685849690 |
| 18 | 5642219814912 |
| 19 | 32071565263710 |
| 20 | 182807922003148 |
| 21 | 1044616697160850 |
[6,18,72,324,1555,7776,39990,209952,1119744, 6046617,32981550,181398528,1004668770,5597440292, 31345665638,176319369216,995685849690, 5642219814912,32071565263710,182807922003148, 1044616697160850] |