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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 34 |
| 4 | 330 |
| 5 | 3381 |
| 6 | 35700 |
| 7 | 384307 |
| 8 | 4193020 |
| 9 | 46203670 |
| 10 | 513011312 |
| 11 | 5730482707 |
| 12 | 64324536822 |
| 13 | 724966763955 |
| 14 | 8198552413800 |
| 15 | 92985865982415 |
| 16 | 1057267681773972 |
| 17 | 12047638469222921 |
| 18 | 137547814582468048 |
| 19 | 1573060924386848400 |
| 20 | 18017644508154675426 |
| 21 | 206653990802794950415 |
[1,4,34,330,3381,35700,384307,4193020,46203670, 513011312,5730482707,64324536822,724966763955, 8198552413800,92985865982415,1057267681773972, 12047638469222921,137547814582468048, 1573060924386848400,18017644508154675426, 206653990802794950415] |