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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 25 |
| 5 | 216 |
| 6 | 1561 |
| 7 | 19328 |
| 8 | 225681 |
| 9 | 3790720 |
| 10 | 54595921 |
| 11 | 1141489152 |
| 12 | 20620975849 |
| 13 | 519551642624 |
| 14 | 11074307974185 |
| 15 | 325796967940096 |
| 16 | 8068953248603809 |
| 17 | 271784019897188352 |
| 18 | 7647972455738262817 |
| 19 | 290140183695205990400 |
| 20 | 9154902981606486123321 |
[1,1,1,4,25,216,1561,19328,225681,3790720, 54595921,1141489152,20620975849,519551642624, 11074307974185,325796967940096,8068953248603809, 271784019897188352,7647972455738262817, 290140183695205990400,9154902981606486123321] |