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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 20 |
| 3 | 104 |
| 4 | 468 |
| 5 | 1960 |
| 6 | 8020 |
| 7 | 32424 |
| 8 | 130388 |
| 9 | 522920 |
| 10 | 2094420 |
| 11 | 8383144 |
| 12 | 33543508 |
| 13 | 134195880 |
| 14 | 536827220 |
| 15 | 2147396264 |
| 16 | 8589759828 |
| 17 | 34359388840 |
| 18 | 137438254420 |
| 19 | 549754415784 |
| 20 | 2199020459348 |
| 21 | 8796087429800 |
| 22 | 35184360904020 |
| 23 | 140737465985704 |
| 24 | 562949908682068 |
[1,2,20,104,468,1960,8020,32424,130388,522920, 2094420,8383144,33543508,134195880,536827220, 2147396264,8589759828,34359388840,137438254420, 549754415784,2199020459348,8796087429800, 35184360904020,140737465985704,562949908682068] |