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| n | a(n) |
|---|---|
| 1 | 20 |
| 2 | 480 |
| 3 | 17680 |
| 4 | 867840 |
| 5 | 53008000 |
| 6 | 3868262400 |
| 7 | 328200070400 |
| 8 | 31743511756800 |
| 9 | 3447768313600000 |
| 10 | 415545796853760000 |
| 11 | 55041558756762624000 |
| 12 | 7948018349009534976000 |
| 13 | 1242718216339451289600000 |
| 14 | 209174003345404408627200000 |
| 15 | 37712045770845433775923200000 |
| 16 | 7250740898779197968241131520000 |
[20,480,17680,867840,53008000,3868262400, 328200070400,31743511756800,3447768313600000, 415545796853760000,55041558756762624000, 7948018349009534976000,1242718216339451289600000, 209174003345404408627200000, 37712045770845433775923200000, 7250740898779197968241131520000] |