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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 26 |
| 4 | 152 |
| 5 | 1132 |
| 6 | 10300 |
| 7 | 111064 |
| 8 | 1387104 |
| 9 | 19713104 |
| 10 | 314350064 |
| 11 | 5560881328 |
| 12 | 108110428288 |
| 13 | 2291750937088 |
| 14 | 52618613073408 |
| 15 | 1301031907140608 |
| 16 | 34470409922547200 |
| 17 | 974354631630161152 |
| 18 | 29270099764874881792 |
| 19 | 931275451933870415104 |
| 20 | 31285710787985504633856 |
[1,2,6,26,152,1132,10300,111064,1387104,19713104, 314350064,5560881328,108110428288,2291750937088, 52618613073408,1301031907140608,34470409922547200, 974354631630161152,29270099764874881792, 931275451933870415104,31285710787985504633856] |