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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 2 |
| 3 | 7 |
| 4 | 20 |
| 5 | 61 |
| 6 | 180 |
| 7 | 543 |
| 8 | 1622 |
| 9 | 4873 |
| 10 | 14598 |
| 11 | 43815 |
| 12 | 131384 |
| 13 | 394213 |
| 14 | 1182456 |
| 15 | 3547551 |
| 16 | 10642110 |
| 17 | 31926873 |
| 18 | 95778990 |
| 19 | 287338599 |
| 20 | 862010924 |
| 21 | 2586037645 |
| 22 | 7758098316 |
| 23 | 23274309567 |
| 24 | 69822884886 |
| 25 | 209468698473 |
| 26 | 628405963974 |
[0,1,2,7,20,61,180,543,1622,4873,14598,43815, 131384,394213,1182456,3547551,10642110,31926873, 95778990,287338599,862010924,2586037645, 7758098316,23274309567,69822884886,209468698473, 628405963974] |