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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 36 |
| 3 | 222 |
| 4 | 1446 |
| 5 | 10116 |
| 6 | 75924 |
| 7 | 602256 |
| 8 | 4958352 |
| 9 | 41783046 |
| 10 | 357442416 |
| 11 | 3091766904 |
| 12 | 26991194550 |
| 13 | 237605649780 |
| 14 | 2107693469880 |
| 15 | 18826297197444 |
| 16 | 169203629332230 |
| 17 | 1529098507275372 |
| 18 | 13885733651626548 |
| 19 | 126641707880226888 |
| 20 | 1159483975207373952 |
| 21 | 10652962589325269040 |
| 22 | 98187525261135608400 |
[1,6,36,222,1446,10116,75924,602256,4958352, 41783046,357442416,3091766904,26991194550, 237605649780,2107693469880,18826297197444, 169203629332230,1529098507275372, 13885733651626548,126641707880226888, 1159483975207373952,10652962589325269040, 98187525261135608400] |