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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 24 |
| 4 | 171 |
| 5 | 1336 |
| 6 | 11060 |
| 7 | 95298 |
| 8 | 845649 |
| 9 | 7675398 |
| 10 | 70921457 |
| 11 | 664905445 |
| 12 | 6309060313 |
| 13 | 60473691666 |
| 14 | 584684295383 |
| 15 | 5695312881404 |
| 16 | 55839455579659 |
| 17 | 550621231581791 |
| 18 | 5457218248143692 |
| 19 | 54332533436452743 |
| 20 | 543148496962279730 |
| 21 | 5449742750024662824 |
[1,1,4,24,171,1336,11060,95298,845649,7675398, 70921457,664905445,6309060313,60473691666, 584684295383,5695312881404,55839455579659, 550621231581791,5457218248143692, 54332533436452743,543148496962279730, 5449742750024662824] |