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| n | a(n) |
|---|---|
| 1 | 6 |
| 2 | 18 |
| 3 | 72 |
| 4 | 324 |
| 5 | 1556 |
| 6 | 7776 |
| 7 | 39991 |
| 8 | 209952 |
| 9 | 1119744 |
| 10 | 6046618 |
| 11 | 32981551 |
| 12 | 181398528 |
| 13 | 1004668771 |
| 14 | 5597440293 |
| 15 | 31345665639 |
| 16 | 176319369216 |
| 17 | 995685849691 |
| 18 | 5642219814912 |
| 19 | 32071565263711 |
| 20 | 182807922003149 |
| 21 | 1044616697160851 |
[6,18,72,324,1556,7776,39991,209952,1119744, 6046618,32981551,181398528,1004668771,5597440293, 31345665639,176319369216,995685849691, 5642219814912,32071565263711,182807922003149, 1044616697160851] |