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| n | a(n) |
|---|---|
| 1 | 108 |
| 2 | 640 |
| 3 | 3500 |
| 4 | 18144 |
| 5 | 90552 |
| 6 | 439296 |
| 7 | 2084940 |
| 8 | 9724000 |
| 9 | 44710952 |
| 10 | 203164416 |
| 11 | 914004728 |
| 12 | 4077035200 |
| 13 | 18052470000 |
| 14 | 79420170240 |
| 15 | 347424465420 |
| 16 | 1512176830560 |
| 17 | 6552247686600 |
| 18 | 28276211040000 |
| 19 | 121580638419240 |
| 20 | 521033622457920 |
[108,640,3500,18144,90552,439296,2084940,9724000, 44710952,203164416,914004728,4077035200, 18052470000,79420170240,347424465420, 1512176830560,6552247686600,28276211040000, 121580638419240,521033622457920] |