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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 21 |
| 4 | 52 |
| 5 | 305 |
| 6 | 7836 |
| 7 | 24703 |
| 8 | 155688 |
| 9 | 1034433 |
| 10 | 67124260 |
| 11 | 235173191 |
| 12 | 1728147312 |
| 13 | 11309344813 |
| 14 | 106962615592 |
| 15 | 14055613872945 |
| 16 | 55558358852176 |
| 17 | 450373499691137 |
| 18 | 3156524223157332 |
| 19 | 28327606849223119 |
| 20 | 307533111218771040 |
| 21 | 81782486813477643501 |
[1,1,2,21,52,305,7836,24703,155688,1034433, 67124260,235173191,1728147312,11309344813, 106962615592,14055613872945,55558358852176, 450373499691137,3156524223157332, 28327606849223119,307533111218771040, 81782486813477643501] |