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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 21 |
| 4 | 85 |
| 5 | 430 |
| 6 | 2586 |
| 7 | 18109 |
| 8 | 144880 |
| 9 | 1303929 |
| 10 | 13039300 |
| 11 | 143432311 |
| 12 | 1721187744 |
| 13 | 22375440685 |
| 14 | 313256169604 |
| 15 | 4698842544075 |
| 16 | 75181480705216 |
| 17 | 1278085171988689 |
| 18 | 23005533095796420 |
| 19 | 437105128820131999 |
| 20 | 8742102576402640000 |
| 21 | 183584154104455440021 |
| 22 | 4038851390298019680484 |
[1,2,6,21,85,430,2586,18109,144880,1303929, 13039300,143432311,1721187744,22375440685, 313256169604,4698842544075,75181480705216, 1278085171988689,23005533095796420, 437105128820131999,8742102576402640000, 183584154104455440021,4038851390298019680484] |