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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 14 |
| 4 | 52 |
| 5 | 220 |
| 6 | 1092 |
| 7 | 6388 |
| 8 | 43588 |
| 9 | 341444 |
| 10 | 3022660 |
| 11 | 29835844 |
| 12 | 324782916 |
| 13 | 3864151876 |
| 14 | 49875956548 |
| 15 | 694041238340 |
| 16 | 10356520497988 |
| 17 | 164956188717892 |
| 18 | 2793150548587332 |
| 19 | 50100649026499396 |
| 20 | 948943120107352900 |
| 21 | 18925792541725471556 |
| 22 | 396439630395708060484 |
[0,1,4,14,52,220,1092,6388,43588,341444,3022660, 29835844,324782916,3864151876,49875956548, 694041238340,10356520497988,164956188717892, 2793150548587332,50100649026499396, 948943120107352900,18925792541725471556, 396439630395708060484] |