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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 3 |
| 3 | 21 |
| 4 | 155 |
| 5 | 1198 |
| 6 | 9840 |
| 7 | 83152 |
| 8 | 720363 |
| 9 | 6356436 |
| 10 | 56882425 |
| 11 | 514755769 |
| 12 | 4700994974 |
| 13 | 43258230232 |
[0,3,21,155,1198,9840,83152,720363,6356436, 56882425,514755769,4700994974,43258230232] |