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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 144 |
| 4 | 2346 |
| 5 | 55236 |
| 6 | 1688084 |
| 7 | 63040736 |
| 8 | 2770165274 |
| 9 | 139623836116 |
| 10 | 7925496107656 |
| 11 | 499719554537584 |
| 12 | 34625595715906866 |
| 13 | 2613946666882042164 |
| 14 | 213475621178226876156 |
| 15 | 18748792440158256161216 |
| 16 | 1761875767691411063734514 |
| 17 | 176383456081424163875684516 |
| 18 | 18739798321516251204837796864 |
| 19 | 2105891800817103192582808107856 |
[1,4,16,144,2346,55236,1688084,63040736, 2770165274,139623836116,7925496107656, 499719554537584,34625595715906866, 2613946666882042164,213475621178226876156, 18748792440158256161216,1761875767691411063734514, 176383456081424163875684516, 18739798321516251204837796864, 2105891800817103192582808107856] |