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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 18 |
| 4 | 191 |
| 5 | 4860 |
| 6 | 310036 |
| 7 | 53350918 |
| 8 | 26097731070 |
| 9 | 37211940860240 |
| 10 | 157260419809121989 |
[0,4,18,191,4860,310036,53350918,26097731070, 37211940860240,157260419809121989] |