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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 24 |
| 4 | 224 |
| 5 | 2880 |
| 6 | 48064 |
| 7 | 989184 |
| 8 | 24218624 |
| 9 | 687083520 |
| 10 | 22151148544 |
| 11 | 799546834944 |
| 12 | 31934834253824 |
| 13 | 1398132497448960 |
| 14 | 66573473015578624 |
| 15 | 3425078687463112704 |
| 16 | 189331392774496845824 |
| 17 | 11190654534195295027200 |
| 18 | 704262689221037166690304 |
| 19 | 47015904809670036594622464 |
| 20 | 3318579148264602406039322624 |
[1,4,24,224,2880,48064,989184,24218624,687083520, 22151148544,799546834944,31934834253824, 1398132497448960,66573473015578624, 3425078687463112704,189331392774496845824, 11190654534195295027200,704262689221037166690304, 47015904809670036594622464, 3318579148264602406039322624] |