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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 9 |
| 4 | 58 |
| 5 | 306 |
| 6 | 1371 |
| 7 | 5451 |
| 8 | 20316 |
| 9 | 73826 |
| 10 | 268227 |
| 11 | 988143 |
| 12 | 3710046 |
| 13 | 14186486 |
| 14 | 55056941 |
| 15 | 215998713 |
| 16 | 853659146 |
| 17 | 3389857782 |
| 18 | 13500951049 |
| 19 | 53867577061 |
[0,2,9,58,306,1371,5451,20316,73826,268227,988143, 3710046,14186486,55056941,215998713,853659146, 3389857782,13500951049,53867577061] |