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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 6 |
| 6 | 24 |
| 7 | 120 |
| 8 | 714 |
| 9 | 4963 |
| 10 | 39520 |
| 11 | 354609 |
| 12 | 3538960 |
| 13 | 38873978 |
| 14 | 466013508 |
| 15 | 6053565700 |
| 16 | 84700374374 |
| 17 | 1269922505955 |
| 18 | 20311303879168 |
| 19 | 345189255328973 |
| 20 | 6211881989182800 |
| 21 | 118001629266860074 |
| 22 | 2359626359259618140 |
[1,1,1,1,2,6,24,120,714,4963,39520,354609,3538960, 38873978,466013508,6053565700,84700374374, 1269922505955,20311303879168,345189255328973, 6211881989182800,118001629266860074, 2359626359259618140] |