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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 18 |
| 3 | 112 |
| 4 | 976 |
| 5 | 11424 |
| 6 | 169936 |
| 7 | 3101032 |
| 8 | 67876608 |
| 9 | 1746757504 |
| 10 | 52034505376 |
| 11 | 1771434644544 |
| 12 | 68180144988928 |
| 13 | 2939951026982272 |
| 14 | 140920461751138176 |
| 15 | 7457658363325181824 |
| 16 | 433145750643704774656 |
| 17 | 27464893679743640343552 |
| 18 | 1892311278990953945563648 |
| 19 | 141074242336048184406390784 |
| 20 | 11336870115013701213795557376 |
[1,4,18,112,976,11424,169936,3101032,67876608, 1746757504,52034505376,1771434644544, 68180144988928,2939951026982272, 140920461751138176,7457658363325181824, 433145750643704774656,27464893679743640343552, 1892311278990953945563648, 141074242336048184406390784, 11336870115013701213795557376] |