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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 42 |
| 3 | 288 |
| 4 | 1980 |
| 5 | 13608 |
| 6 | 93528 |
| 7 | 642816 |
| 8 | 4418064 |
| 9 | 30365280 |
| 10 | 208700064 |
| 11 | 1434392064 |
| 12 | 9858552768 |
| 13 | 67757668992 |
| 14 | 465697330560 |
| 15 | 3200729997312 |
| 16 | 21998563967232 |
| 17 | 151195763787264 |
| 18 | 1039165966526976 |
| 19 | 7142170381885440 |
[1,6,42,288,1980,13608,93528,642816,4418064, 30365280,208700064,1434392064,9858552768, 67757668992,465697330560,3200729997312, 21998563967232,151195763787264,1039165966526976, 7142170381885440] |