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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 5 |
| 3 | 20 |
| 4 | 105 |
| 5 | 520 |
| 6 | 2605 |
| 7 | 13020 |
| 8 | 65105 |
| 9 | 325520 |
| 10 | 1627605 |
| 11 | 8138020 |
| 12 | 40690105 |
| 13 | 203450520 |
| 14 | 1017252605 |
| 15 | 5086263020 |
| 16 | 25431315105 |
| 17 | 127156575520 |
| 18 | 635782877605 |
| 19 | 3178914388020 |
| 20 | 15894571940105 |
| 21 | 79472859700520 |
[1,0,5,20,105,520,2605,13020,65105,325520,1627605, 8138020,40690105,203450520,1017252605,5086263020, 25431315105,127156575520,635782877605, 3178914388020,15894571940105,79472859700520] |