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| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 5 |
| 3 | 20 |
| 4 | 51 |
| 5 | 312 |
| 6 | 740 |
| 7 | 15000 |
| 8 | 34125 |
| 9 | 160720 |
| 10 | 4988592 |
| 11 | 180774720 |
| 12 | 844074000 |
| 13 | 27991656000 |
| 14 | 66264953040 |
[2,5,20,51,312,740,15000,34125,160720,4988592, 180774720,844074000,27991656000,66264953040] |