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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 24 |
| 4 | 171 |
| 5 | 1338 |
| 6 | 11109 |
| 7 | 96100 |
| 8 | 856762 |
| 9 | 7816616 |
| 10 | 72627241 |
| 11 | 684859147 |
| 12 | 6537520290 |
| 13 | 63050669143 |
| 14 | 613441446154 |
| 15 | 6013687144000 |
| 16 | 59343220508344 |
| 17 | 589004488233064 |
| 18 | 5876204912724812 |
| 19 | 58893312496308755 |
| 20 | 592682966496901253 |
| 21 | 5986771171677305889 |
| 22 | 60677419447552591497 |
[1,1,4,24,171,1338,11109,96100,856762,7816616, 72627241,684859147,6537520290,63050669143, 613441446154,6013687144000,59343220508344, 589004488233064,5876204912724812, 58893312496308755,592682966496901253, 5986771171677305889,60677419447552591497] |