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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 18 |
| 4 | 219 |
| 5 | 4395 |
| 6 | 129280 |
| 7 | 4970984 |
| 8 | 257765641 |
| 9 | 16781325293 |
| 10 | 1348125117404 |
| 11 | 132465548869248 |
| 12 | 15490711962965785 |
| 13 | 2134540479514352751 |
| 14 | 343307151209151099650 |
| 15 | 63606662918084631874716 |
| 16 | 13470938654397531939066909 |
| 17 | 3238387688528230753569245297 |
| 18 | 876825599524773154743990986391 |
[1,1,2,18,219,4395,129280,4970984,257765641, 16781325293,1348125117404,132465548869248, 15490711962965785,2134540479514352751, 343307151209151099650,63606662918084631874716, 13470938654397531939066909, 3238387688528230753569245297, 876825599524773154743990986391] |