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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 12 |
| 3 | 54 |
| 4 | 265 |
| 5 | 1401 |
| 6 | 7903 |
| 7 | 47088 |
| 8 | 293319 |
| 9 | 1892440 |
| 10 | 12548041 |
| 11 | 84988566 |
| 12 | 585314652 |
| 13 | 4085026386 |
| 14 | 28820064810 |
| 15 | 205156454376 |
| 16 | 1471492171068 |
| 17 | 10622954509803 |
| 18 | 77122189800121 |
| 19 | 562684397212060 |
| 20 | 4123449352097229 |
| 21 | 30336562360256955 |
[1,3,12,54,265,1401,7903,47088,293319,1892440, 12548041,84988566,585314652,4085026386, 28820064810,205156454376,1471492171068, 10622954509803,77122189800121,562684397212060, 4123449352097229,30336562360256955] |