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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | 9 |
| 4 | 30 |
| 5 | 99 |
| 6 | 333 |
| 7 | 1144 |
| 8 | 3978 |
| 9 | 13995 |
| 10 | 49742 |
| 11 | 178296 |
| 12 | 643842 |
| 13 | 2340135 |
| 14 | 8554275 |
| 15 | 31429026 |
| 16 | 115997970 |
| 17 | 429874830 |
| 18 | 1598952366 |
| 19 | 5967382200 |
| 20 | 22338765540 |
| 21 | 83859016527 |
| 22 | 315614844558 |
| 23 | 1190680751376 |
| 24 | 4501802223090 |
| 25 | 17055399281284 |
[0,1,3,9,30,99,333,1144,3978,13995,49742,178296, 643842,2340135,8554275,31429026,115997970, 429874830,1598952366,5967382200,22338765540, 83859016527,315614844558,1190680751376, 4501802223090,17055399281284] |