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| n | a(n) |
|---|---|
| 0 | 2 |
| 1 | 3 |
| 2 | 6 |
| 3 | 17 |
| 4 | 66 |
| 5 | 327 |
| 6 | 1958 |
| 7 | 13701 |
| 8 | 109602 |
| 9 | 986411 |
| 10 | 9864102 |
| 11 | 108505113 |
| 12 | 1302061346 |
| 13 | 16926797487 |
| 14 | 236975164806 |
| 15 | 3554627472077 |
| 16 | 56874039553218 |
| 17 | 966858672404691 |
| 18 | 17403456103284422 |
| 19 | 330665665962404001 |
| 20 | 6613313319248080002 |
[2,3,6,17,66,327,1958,13701,109602,986411,9864102, 108505113,1302061346,16926797487,236975164806, 3554627472077,56874039553218,966858672404691, 17403456103284422,330665665962404001, 6613313319248080002] |