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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 36 |
| 3 | 364 |
| 4 | 3876 |
| 5 | 42504 |
| 6 | 475020 |
| 7 | 5379616 |
| 8 | 61523748 |
| 9 | 708930508 |
| 10 | 8217822536 |
| 11 | 95722852680 |
| 12 | 1119487075980 |
| 13 | 13136858812224 |
| 14 | 154603005527328 |
| 15 | 1824010149372864 |
| 16 | 21566576904406820 |
| 17 | 255485622301674660 |
| 18 | 3031718514166879020 |
| 19 | 36030431772522503316 |
[1,4,36,364,3876,42504,475020,5379616,61523748, 708930508,8217822536,95722852680,1119487075980, 13136858812224,154603005527328,1824010149372864, 21566576904406820,255485622301674660, 3031718514166879020,36030431772522503316] |