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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 9 |
| 3 | 55 |
| 4 | 345 |
| 5 | 2236 |
| 6 | 14727 |
| 7 | 98134 |
| 8 | 659801 |
| 9 | 4467160 |
| 10 | 30413924 |
| 11 | 208016337 |
| 12 | 1428159207 |
| 13 | 9836845630 |
| 14 | 67941521286 |
| 15 | 470386502500 |
| 16 | 3263507004569 |
| 17 | 22683873869360 |
| 18 | 157929616709400 |
| 19 | 1101154915382352 |
| 20 | 7687901741554980 |
| 21 | 53738680702979509 |
| 22 | 376043976132232153 |
[1,1,9,55,345,2236,14727,98134,659801,4467160, 30413924,208016337,1428159207,9836845630, 67941521286,470386502500,3263507004569, 22683873869360,157929616709400,1101154915382352, 7687901741554980,53738680702979509, 376043976132232153] |