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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 51 |
| 4 | 588 |
| 5 | 7990 |
| 6 | 126060 |
| 7 | 2242618 |
| 8 | 44546320 |
| 9 | 977152266 |
| 10 | 23500234512 |
| 11 | 615372604033 |
| 12 | 17442275104496 |
| 13 | 532242021137346 |
| 14 | 17399782340548920 |
| 15 | 606732491690590816 |
| 16 | 22477989291826848000 |
| 17 | 881635273413199806994 |
| 18 | 36493478646922003374096 |
| 19 | 1589642562747880936613248 |
[1,1,6,51,588,7990,126060,2242618,44546320, 977152266,23500234512,615372604033,17442275104496, 532242021137346,17399782340548920, 606732491690590816,22477989291826848000, 881635273413199806994,36493478646922003374096, 1589642562747880936613248] |