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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 27 |
| 4 | 255 |
| 5 | 3028 |
| 6 | 41979 |
| 7 | 647790 |
| 8 | 10803237 |
| 9 | 191122140 |
| 10 | 3542732908 |
| 11 | 68213661464 |
| 12 | 1355643940248 |
| 13 | 27673150807344 |
| 14 | 578051855658450 |
| 15 | 12318499151821116 |
| 16 | 267156147212406393 |
| 17 | 5884501351433388108 |
| 18 | 131418738987996420708 |
| 19 | 2971588663914996425000 |
[1,1,4,27,255,3028,41979,647790,10803237, 191122140,3542732908,68213661464,1355643940248, 27673150807344,578051855658450,12318499151821116, 267156147212406393,5884501351433388108, 131418738987996420708,2971588663914996425000] |