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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 36 |
| 4 | 384 |
| 5 | 5125 |
| 6 | 81864 |
| 7 | 1519833 |
| 8 | 32219136 |
| 9 | 768352149 |
| 10 | 20367510000 |
| 11 | 594270942705 |
| 12 | 18929706034176 |
| 13 | 653744865197242 |
| 14 | 24333393186194848 |
| 15 | 971177936039212500 |
| 16 | 41376191798281502720 |
| 17 | 1874320475909920820607 |
| 18 | 89961819584112859211712 |
| 19 | 4560744533588836253021837 |
[1,1,4,36,384,5125,81864,1519833,32219136, 768352149,20367510000,594270942705,18929706034176, 653744865197242,24333393186194848, 971177936039212500,41376191798281502720, 1874320475909920820607,89961819584112859211712, 4560744533588836253021837] |