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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 24 |
| 5 | 116 |
| 6 | 657 |
| 7 | 4260 |
| 8 | 31144 |
| 9 | 253400 |
| 10 | 2271250 |
| 11 | 22234380 |
| 12 | 236042879 |
| 13 | 2700973070 |
| 14 | 33139335352 |
| 15 | 433996381926 |
| 16 | 6042468288640 |
| 17 | 89124117755852 |
| 18 | 1388234052651161 |
| 19 | 22771513253008320 |
| 20 | 392354340340237176 |
| 21 | 7084700602143004688 |
| 22 | 133785708212530414358 |
| 23 | 2636998678988431607188 |
[1,1,2,6,24,116,657,4260,31144,253400,2271250, 22234380,236042879,2700973070,33139335352, 433996381926,6042468288640,89124117755852, 1388234052651161,22771513253008320, 392354340340237176,7084700602143004688, 133785708212530414358,2636998678988431607188] |