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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 3 |
| 3 | 18 |
| 4 | 215 |
| 5 | 3600 |
| 6 | 80136 |
| 7 | 2213036 |
| 8 | 73068543 |
| 9 | 2806959015 |
| 10 | 123002168300 |
| 11 | 6055381161852 |
| 12 | 330885794632536 |
| 13 | 19872950226273053 |
| 14 | 1301261803764756855 |
| 15 | 92259974680854975000 |
| 16 | 7041606755629152575055 |
| 17 | 575638367425376279620662 |
| 18 | 50180725346542105445190603 |
[1,3,18,215,3600,80136,2213036,73068543, 2806959015,123002168300,6055381161852, 330885794632536,19872950226273053, 1301261803764756855,92259974680854975000, 7041606755629152575055,575638367425376279620662, 50180725346542105445190603] |