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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 20 |
| 3 | 180 |
| 4 | 1722 |
| 5 | 15484 |
| 6 | 129914 |
| 7 | 1079792 |
| 8 | 8845592 |
| 9 | 71540206 |
| 10 | 572555634 |
| 11 | 4544198480 |
| 12 | 35814522446 |
| 13 | 280584310722 |
| 14 | 2186897305592 |
| 15 | 16968580781888 |
| 16 | 131145107324352 |
| 17 | 1010053181919720 |
| 18 | 7755079215544062 |
| 19 | 59376833021426668 |
[2,20,180,1722,15484,129914,1079792,8845592, 71540206,572555634,4544198480,35814522446, 280584310722,2186897305592,16968580781888, 131145107324352,1010053181919720,7755079215544062, 59376833021426668] |