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| n | a(n) |
|---|---|
| -1 | 0 |
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 10 |
| 4 | 32 |
| 5 | 126 |
| 6 | 588 |
| 7 | 3170 |
| 8 | 19384 |
| 9 | 132550 |
| 10 | 1002212 |
| 11 | 8301930 |
| 12 | 74767056 |
| 13 | 727348814 |
| 14 | 7601002876 |
| 15 | 84920459890 |
| 16 | 1010058659048 |
| 17 | 12742908917718 |
| 18 | 169962226236180 |
| 19 | 2389587638934650 |
| 20 | 35321010036943360 |
| 21 | 547577222471444062 |
[0,1,2,4,10,32,126,588,3170,19384,132550,1002212, 8301930,74767056,727348814,7601002876,84920459890, 1010058659048,12742908917718,169962226236180, 2389587638934650,35321010036943360, 547577222471444062] |