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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 10 |
| 3 | 80 |
| 4 | 750 |
| 5 | 7680 |
| 6 | 83252 |
| 7 | 939008 |
| 8 | 10905942 |
| 9 | 129548288 |
| 10 | 1566565452 |
| 11 | 19220267008 |
| 12 | 238662840780 |
| 13 | 2993651974144 |
| 14 | 37876206019560 |
| 15 | 482802294325248 |
| 16 | 6194365014836582 |
| 17 | 79930063134392320 |
| 18 | 1036640587694252380 |
| 19 | 13505632613590630400 |
| 20 | 176673045664669396132 |
| 21 | 2319654465118014537728 |
[1,2,10,80,750,7680,83252,939008,10905942, 129548288,1566565452,19220267008,238662840780, 2993651974144,37876206019560,482802294325248, 6194365014836582,79930063134392320, 1036640587694252380,13505632613590630400, 176673045664669396132,2319654465118014537728] |