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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 30 |
| 5 | 305 |
| 6 | 3905 |
| 7 | 59828 |
| 8 | 1063728 |
| 9 | 21497921 |
| 10 | 486476766 |
| 11 | 12184618776 |
| 12 | 334684804952 |
| 13 | 10005219881472 |
| 14 | 323438539163521 |
| 15 | 11244331792094312 |
| 16 | 418375698771595037 |
| 17 | 16590419690069321454 |
| 18 | 698526596162530976512 |
[1,1,1,4,30,305,3905,59828,1063728,21497921, 486476766,12184618776,334684804952,10005219881472, 323438539163521,11244331792094312, 418375698771595037,16590419690069321454, 698526596162530976512] |