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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 6 |
| 3 | 70 |
| 4 | 1050 |
| 5 | 18018 |
| 6 | 336336 |
| 7 | 6651216 |
| 8 | 137181330 |
| 9 | 2921454250 |
| 10 | 63804560820 |
| 11 | 1422156202740 |
| 12 | 32235540595440 |
| 13 | 741035948007600 |
| 14 | 17240428178136000 |
| 15 | 405264998374050240 |
| 16 | 9612379180184504130 |
| 17 | 229799057978874529530 |
| 18 | 5532199543935868303500 |
| 19 | 134014085905039247407500 |
[1,6,70,1050,18018,336336,6651216,137181330, 2921454250,63804560820,1422156202740, 32235540595440,741035948007600,17240428178136000, 405264998374050240,9612379180184504130, 229799057978874529530,5532199543935868303500, 134014085905039247407500] |