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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 20 |
| 4 | 182 |
| 5 | 1640 |
| 6 | 14762 |
| 7 | 132860 |
| 8 | 1195742 |
| 9 | 10761680 |
| 10 | 96855122 |
| 11 | 871696100 |
| 12 | 7845264902 |
| 13 | 70607384120 |
| 14 | 635466457082 |
| 15 | 5719198113740 |
| 16 | 51472783023662 |
| 17 | 463255047212960 |
| 18 | 4169295424916642 |
| 19 | 37523658824249780 |
| 20 | 337712929418248022 |
[0,2,20,182,1640,14762,132860,1195742,10761680, 96855122,871696100,7845264902,70607384120, 635466457082,5719198113740,51472783023662, 463255047212960,4169295424916642, 37523658824249780,337712929418248022] |