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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 9 |
| 5 | 45 |
| 6 | 225 |
| 7 | 1575 |
| 8 | 11024 |
| 9 | 99216 |
| 10 | 891984 |
| 11 | 9811824 |
| 12 | 107544862 |
| 13 | 1398083206 |
| 14 | 18043262766 |
| 15 | 270648941490 |
| 16 | 4013029762464 |
| 17 | 68221505961888 |
| 18 | 1141412702224688 |
| 19 | 21686841342269072 |
| 20 | 403841897925538896 |
| 21 | 8480679856436316816 |
| 22 | 173881330973591388704 |
[1,1,1,3,9,45,225,1575,11024,99216,891984,9811824, 107544862,1398083206,18043262766,270648941490, 4013029762464,68221505961888,1141412702224688, 21686841342269072,403841897925538896, 8480679856436316816,173881330973591388704] |