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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 18 |
| 3 | 144 |
| 4 | 1323 |
| 5 | 13176 |
| 6 | 138348 |
| 7 | 1507977 |
| 8 | 16900650 |
| 9 | 193536864 |
| 10 | 2254630788 |
| 11 | 26635735440 |
| 12 | 318350663748 |
| 13 | 3842488208997 |
| 14 | 46770206742342 |
| 15 | 573435609537600 |
| 16 | 7075551692662875 |
| 17 | 87794803094586336 |
| 18 | 1094807464312435344 |
[1,3,18,144,1323,13176,138348,1507977,16900650, 193536864,2254630788,26635735440,318350663748, 3842488208997,46770206742342,573435609537600, 7075551692662875,87794803094586336, 1094807464312435344] |