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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 4 |
| 4 | 57 |
| 5 | 348 |
| 6 | 5235 |
| 7 | 57930 |
| 8 | 1037540 |
| 9 | 16842496 |
| 10 | 363889755 |
| 11 | 7792175070 |
| 12 | 201054289293 |
| 13 | 5345844537876 |
| 14 | 162234861271288 |
| 15 | 5156725529935952 |
| 16 | 181284205622239755 |
| 17 | 6713109719185427600 |
| 18 | 269652617328843102055 |
| 19 | 11418447984579685481310 |
| 20 | 517839485352765454438270 |
[1,0,2,4,57,348,5235,57930,1037540,16842496, 363889755,7792175070,201054289293,5345844537876, 162234861271288,5156725529935952, 181284205622239755,6713109719185427600, 269652617328843102055,11418447984579685481310, 517839485352765454438270] |