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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 48 |
| 4 | 442 |
| 5 | 4419 |
| 6 | 46626 |
| 7 | 511032 |
| 8 | 5761650 |
| 9 | 66394596 |
| 10 | 778518552 |
| 11 | 9258850440 |
| 12 | 111417705702 |
| 13 | 1354135251538 |
| 14 | 16598001854700 |
| 15 | 204945037918800 |
| 16 | 2546849778687138 |
| 17 | 31828936270676172 |
| 18 | 399777371427582024 |
| 19 | 5043824569861127808 |
| 20 | 63892650400004356776 |
[1,1,6,48,442,4419,46626,511032,5761650,66394596, 778518552,9258850440,111417705702,1354135251538, 16598001854700,204945037918800,2546849778687138, 31828936270676172,399777371427582024, 5043824569861127808,63892650400004356776] |