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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 6 |
| 3 | 57 |
| 4 | 752 |
| 5 | 12730 |
| 6 | 263172 |
| 7 | 6427239 |
| 8 | 181073552 |
| 9 | 5780683422 |
| 10 | 206236365320 |
| 11 | 8131806499806 |
| 12 | 351152348814720 |
| 13 | 16481622338583844 |
| 14 | 835440526931000200 |
| 15 | 45483669552645222975 |
| 16 | 2646983711809388956320 |
| 17 | 163980758725017626674422 |
| 18 | 10774158375350926668928248 |
[1,1,6,57,752,12730,263172,6427239,181073552, 5780683422,206236365320,8131806499806, 351152348814720,16481622338583844, 835440526931000200,45483669552645222975, 2646983711809388956320,163980758725017626674422, 10774158375350926668928248] |