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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 4 |
| 3 | 20 |
| 4 | 85 |
| 5 | 344 |
| 6 | 1365 |
| 7 | 5368 |
| 8 | 21021 |
| 9 | 82160 |
| 10 | 320892 |
| 11 | 1253240 |
| 12 | 4896034 |
| 13 | 19137104 |
| 14 | 74847175 |
| 15 | 292929840 |
| 16 | 1147223325 |
| 17 | 4496006880 |
| 18 | 17631691440 |
| 19 | 69189377400 |
| 20 | 271676550390 |
| 21 | 1067383059600 |
| 22 | 4195964793930 |
| 23 | 16503454480656 |
| 24 | 64943823784050 |
| 25 | 255687666536224 |
[0,0,4,20,85,344,1365,5368,21021,82160,320892, 1253240,4896034,19137104,74847175,292929840, 1147223325,4496006880,17631691440,69189377400, 271676550390,1067383059600,4195964793930, 16503454480656,64943823784050,255687666536224] |