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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 16 |
| 4 | 65 |
| 5 | 265 |
| 6 | 1081 |
| 7 | 4410 |
| 8 | 17991 |
| 9 | 73396 |
| 10 | 299426 |
| 11 | 1221537 |
| 12 | 4983377 |
| 13 | 20330163 |
| 14 | 82938844 |
| 15 | 338356945 |
| 16 | 1380359512 |
| 17 | 5631308624 |
| 18 | 22973462017 |
| 19 | 93722435101 |
| 20 | 382349636061 |
| 21 | 1559831901918 |
| 22 | 6363483400447 |
| 23 | 25960439030624 |
[0,1,4,16,65,265,1081,4410,17991,73396,299426, 1221537,4983377,20330163,82938844,338356945, 1380359512,5631308624,22973462017,93722435101, 382349636061,1559831901918,6363483400447, 25960439030624] |