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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 7 |
| 3 | 41 |
| 4 | 290 |
| 5 | 2074 |
| 6 | 18444 |
| 7 | 165108 |
| 8 | 1749264 |
| 9 | 19412496 |
| 10 | 241299360 |
| 11 | 3097006560 |
| 12 | 45546606720 |
| 13 | 673536159360 |
| 14 | 10986261431040 |
| 15 | 187460277177600 |
| 16 | 3445281394329600 |
| 17 | 64637392771123200 |
| 18 | 1325310849663897600 |
| 19 | 27498565425087590400 |
| 20 | 616389533324974080000 |
[1,7,41,290,2074,18444,165108,1749264,19412496, 241299360,3097006560,45546606720,673536159360, 10986261431040,187460277177600,3445281394329600, 64637392771123200,1325310849663897600, 27498565425087590400,616389533324974080000] |