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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 7 |
| 4 | 31 |
| 5 | 157 |
| 6 | 865 |
| 7 | 5051 |
| 8 | 30774 |
| 9 | 193669 |
| 10 | 1250319 |
| 11 | 8240232 |
| 12 | 55239187 |
| 13 | 375624781 |
| 14 | 2585449450 |
| 15 | 17982937876 |
| 16 | 126222946496 |
| 17 | 893073250063 |
| 18 | 6363674671524 |
| 19 | 45631735776036 |
| 20 | 329065051395940 |
| 21 | 2385126419825231 |
[1,1,2,7,31,157,865,5051,30774,193669,1250319, 8240232,55239187,375624781,2585449450,17982937876, 126222946496,893073250063,6363674671524, 45631735776036,329065051395940,2385126419825231] |