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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 25 |
| 4 | 211 |
| 5 | 2238 |
| 6 | 28560 |
| 7 | 425808 |
| 8 | 7261200 |
| 9 | 139367278 |
| 10 | 2973006344 |
| 11 | 69775267186 |
| 12 | 1786673529746 |
| 13 | 49565881948204 |
| 14 | 1480900541242572 |
| 15 | 47407364553205448 |
| 16 | 1618838460981098680 |
| 17 | 58734896900587841824 |
| 18 | 2256402484187691207152 |
| 19 | 91499934912942249975504 |
| 20 | 3905739517580787866827872 |
[1,1,4,25,211,2238,28560,425808,7261200,139367278, 2973006344,69775267186,1786673529746, 49565881948204,1480900541242572,47407364553205448, 1618838460981098680,58734896900587841824, 2256402484187691207152,91499934912942249975504, 3905739517580787866827872] |