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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 3 |
| 3 | 12 |
| 4 | 90 |
| 5 | 816 |
| 6 | 9206 |
| 7 | 122028 |
| 8 | 1859550 |
| 9 | 32002076 |
| 10 | 613891800 |
| 11 | 12989299596 |
| 12 | 300556868286 |
| 13 | 7550646317520 |
| 14 | 204687481411974 |
| 15 | 5955892982437120 |
| 16 | 185158929517924710 |
| 17 | 6125200081143892800 |
| 18 | 214837724609534836158 |
| 19 | 7963817560398871790604 |
| 20 | 311101285877490394183800 |
| 21 | 12773912991134665452205048 |
[1,3,12,90,816,9206,122028,1859550,32002076, 613891800,12989299596,300556868286,7550646317520, 204687481411974,5955892982437120, 185158929517924710,6125200081143892800, 214837724609534836158,7963817560398871790604, 311101285877490394183800, 12773912991134665452205048] |