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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 36 |
| 3 | 324 |
| 4 | 2916 |
| 5 | 26244 |
| 6 | 236196 |
| 7 | 2125764 |
| 8 | 19131876 |
| 9 | 172186884 |
| 10 | 1549681956 |
| 11 | 13947137604 |
| 12 | 125524238436 |
| 13 | 1129718145924 |
| 14 | 10167463313316 |
| 15 | 91507169819844 |
| 16 | 823564528378596 |
| 17 | 7412080755407364 |
| 18 | 66708726798666276 |
| 19 | 600378541187996484 |
| 20 | 5403406870691968356 |
| 21 | 48630661836227715204 |
[1,4,36,324,2916,26244,236196,2125764,19131876, 172186884,1549681956,13947137604,125524238436, 1129718145924,10167463313316,91507169819844, 823564528378596,7412080755407364, 66708726798666276,600378541187996484, 5403406870691968356,48630661836227715204] |