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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 6 |
| 3 | 56 |
| 4 | 448 |
| 5 | 6264 |
| 6 | 96348 |
| 7 | 1559520 |
| 8 | 16908804 |
| 9 | 391945400 |
| 10 | 20553536052 |
| 11 | 706019328000 |
| 12 | 20210523379200 |
| 13 | 519285252355776 |
| 14 | 21710734431216480 |
| 15 | 1456143373228677120 |
| 16 | 25536237889612326912 |
| 17 | 1792353900753729655758 |
| 18 | 52839150354952425838080 |
| 19 | 4154723599066412190910560 |
[1,6,56,448,6264,96348,1559520,16908804,391945400, 20553536052,706019328000,20210523379200, 519285252355776,21710734431216480, 1456143373228677120,25536237889612326912, 1792353900753729655758,52839150354952425838080, 4154723599066412190910560] |