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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 24 |
| 4 | 122 |
| 5 | 750 |
| 6 | 5376 |
| 7 | 43856 |
| 8 | 400518 |
| 9 | 4046334 |
| 10 | 44808104 |
| 11 | 539850984 |
| 12 | 7032370302 |
| 13 | 98516491214 |
| 14 | 1477264979352 |
| 15 | 23612920280976 |
| 16 | 400847064718166 |
| 17 | 7202901369491694 |
| 18 | 136596819590256984 |
| 19 | 2726503675380494408 |
[1,2,6,24,122,750,5376,43856,400518,4046334, 44808104,539850984,7032370302,98516491214, 1477264979352,23612920280976,400847064718166, 7202901369491694,136596819590256984, 2726503675380494408] |