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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 7 |
| 5 | 36 |
| 6 | 171 |
| 7 | 813 |
| 8 | 4012 |
| 9 | 25931 |
| 10 | 342263 |
| 11 | 6498746 |
| 12 | 116477549 |
| 13 | 1839530421 |
| 14 | 26071946330 |
| 15 | 339710531761 |
| 16 | 4165394873379 |
| 17 | 50578180795388 |
| 18 | 717354862704287 |
| 19 | 15348610400624113 |
| 20 | 466529833772501084 |
| 21 | 15332096138370552335 |
[0,0,1,7,36,171,813,4012,25931,342263,6498746, 116477549,1839530421,26071946330,339710531761, 4165394873379,50578180795388,717354862704287, 15348610400624113,466529833772501084, 15332096138370552335] |