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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 18 |
| 5 | 81 |
| 6 | 338 |
| 7 | 1384 |
| 8 | 5588 |
| 9 | 22405 |
| 10 | 89430 |
| 11 | 355906 |
| 12 | 1413600 |
| 13 | 5607109 |
| 14 | 22220902 |
| 15 | 88008656 |
| 16 | 348435254 |
| 17 | 1379169043 |
| 18 | 5458320734 |
| 19 | 21601368452 |
| 20 | 85488832259 |
| 21 | 338346669389 |
| 22 | 1339221309614 |
| 23 | 5301399720197 |
| 24 | 20988604614673 |
| 25 | 83106763866881 |
| 26 | 329118546749196 |
| 27 | 1303568050309469 |
| 28 | 5163945978762924 |
[0,0,0,4,18,81,338,1384,5588,22405,89430,355906, 1413600,5607109,22220902,88008656,348435254, 1379169043,5458320734,21601368452,85488832259, 338346669389,1339221309614,5301399720197, 20988604614673,83106763866881,329118546749196, 1303568050309469,5163945978762924] |