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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 22 |
| 4 | 155 |
| 5 | 1333 |
| 6 | 13541 |
| 7 | 158688 |
| 8 | 2107682 |
| 9 | 31291894 |
| 10 | 513590170 |
| 11 | 9234669420 |
| 12 | 180534475832 |
| 13 | 3812852144788 |
| 14 | 86517295628188 |
| 15 | 2099170738243328 |
| 16 | 54233876338638192 |
| 17 | 1486517654443664016 |
| 18 | 43084555863325589232 |
| 19 | 1316588795487600071904 |
| 20 | 42306543064537291007424 |
| 21 | 1426115146736949130634400 |
[0,1,4,22,155,1333,13541,158688,2107682,31291894, 513590170,9234669420,180534475832,3812852144788, 86517295628188,2099170738243328,54233876338638192, 1486517654443664016,43084555863325589232, 1316588795487600071904,42306543064537291007424, 1426115146736949130634400] |