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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 26 |
| 3 | 300 |
| 4 | 4134 |
| 5 | 61696 |
| 6 | 969660 |
| 7 | 15837400 |
| 8 | 266125823 |
| 9 | 4571229248 |
| 10 | 79904206064 |
| 11 | 1416736880104 |
| 12 | 25418030469904 |
| 13 | 460600399886240 |
| 14 | 8417980252615072 |
| 15 | 154985730303047328 |
| 16 | 2871904782258356719 |
| 17 | 53519211809275995362 |
| 18 | 1002383232008661189884 |
| 19 | 18858606600633628740774 |
[1,4,26,300,4134,61696,969660,15837400,266125823, 4571229248,79904206064,1416736880104, 25418030469904,460600399886240,8417980252615072, 154985730303047328,2871904782258356719, 53519211809275995362,1002383232008661189884, 18858606600633628740774] |