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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 5 |
| 2 | 40 |
| 3 | 320 |
| 4 | 2660 |
| 5 | 23455 |
| 6 | 216540 |
| 7 | 2064055 |
| 8 | 20137945 |
| 9 | 200134600 |
| 10 | 2019406895 |
| 11 | 20635313325 |
| 12 | 213109960895 |
| 13 | 2220820915065 |
| 14 | 23323755734820 |
| 15 | 246616999661690 |
| 16 | 2623193780773530 |
| 17 | 28049464032800110 |
| 18 | 301340494687086960 |
| 19 | 3251017466141039095 |
| 20 | 35207152686408604400 |
[1,5,40,320,2660,23455,216540,2064055,20137945, 200134600,2019406895,20635313325,213109960895, 2220820915065,23323755734820,246616999661690, 2623193780773530,28049464032800110, 301340494687086960,3251017466141039095, 35207152686408604400] |