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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 25 |
| 5 | 125 |
| 6 | 633 |
| 7 | 2532 |
| 8 | 10288 |
| 9 | 48776 |
| 10 | 233776 |
| 11 | 1080228 |
| 12 | 4996113 |
| 13 | 23080949 |
| 14 | 107157345 |
| 15 | 501507348 |
| 16 | 2345998289 |
| 17 | 10947914825 |
| 18 | 51111745065 |
| 19 | 238823109920 |
| 20 | 1116507049088 |
| 21 | 5221116919456 |
| 22 | 24414616690816 |
| 23 | 114158428564416 |
[1,1,4,25,125,633,2532,10288,48776,233776,1080228, 4996113,23080949,107157345,501507348,2345998289, 10947914825,51111745065,238823109920, 1116507049088,5221116919456,24414616690816, 114158428564416] |