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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 5 |
| 4 | 15 |
| 5 | 52 |
| 6 | 203 |
| 7 | 877 |
| 8 | 4140 |
| 9 | 21147 |
| 10 | 115975 |
| 11 | 678569 |
| 12 | 4213546 |
| 13 | 27642948 |
| 14 | 190866373 |
| 15 | 1382340849 |
| 16 | 10469739750 |
| 17 | 82701857286 |
| 18 | 679644668584 |
| 19 | 5797647603036 |
| 20 | 51228938289039 |
| 21 | 467980667203765 |
[1,1,2,5,15,52,203,877,4140,21147,115975,678569, 4213546,27642948,190866373,1382340849,10469739750, 82701857286,679644668584,5797647603036, 51228938289039,467980667203765] |