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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 8 |
| 4 | 28 |
| 5 | 104 |
| 6 | 396 |
| 7 | 1504 |
| 8 | 5720 |
| 9 | 21872 |
| 10 | 83980 |
| 11 | 323344 |
| 12 | 1248072 |
| 13 | 4828784 |
| 14 | 18721080 |
| 15 | 72711552 |
| 16 | 282861360 |
| 17 | 1101980000 |
| 18 | 4298748300 |
| 19 | 16789002736 |
| 20 | 65641204200 |
| 21 | 256895795312 |
| 22 | 1006308200040 |
| 23 | 3945185586368 |
| 24 | 15478849767888 |
| 25 | 60774329914144 |
| 26 | 238775589937976 |
[1,0,2,8,28,104,396,1504,5720,21872,83980,323344, 1248072,4828784,18721080,72711552,282861360, 1101980000,4298748300,16789002736,65641204200, 256895795312,1006308200040,3945185586368, 15478849767888,60774329914144,238775589937976] |