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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 24 |
| 3 | 116 |
| 4 | 568 |
| 5 | 2500 |
| 6 | 10176 |
| 7 | 41116 |
| 8 | 164728 |
| 9 | 658292 |
| 10 | 2623192 |
| 11 | 10451916 |
| 12 | 41644088 |
| 13 | 166056252 |
| 14 | 662379024 |
| 15 | 2643704140 |
[1,4,24,116,568,2500,10176,41116,164728,658292, 2623192,10451916,41644088,166056252,662379024, 2643704140] |