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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 8 |
| 2 | 52 |
| 3 | 264 |
| 4 | 1194 |
| 5 | 4872 |
| 6 | 18516 |
| 7 | 66264 |
| 8 | 226083 |
| 9 | 740608 |
| 10 | 2344232 |
| 11 | 7202416 |
| 12 | 21562164 |
| 13 | 63090288 |
| 14 | 180884088 |
| 15 | 509245776 |
| 16 | 1410356133 |
| 17 | 3848340312 |
| 18 | 10359516684 |
| 19 | 27544099704 |
| 20 | 72406891326 |
| 21 | 188356187448 |
[1,8,52,264,1194,4872,18516,66264,226083,740608, 2344232,7202416,21562164,63090288,180884088, 509245776,1410356133,3848340312,10359516684, 27544099704,72406891326,188356187448] |