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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 9 |
| 5 | 34 |
| 6 | 71 |
| 7 | 245 |
| 8 | 543 |
| 9 | 1835 |
| 10 | 4223 |
| 11 | 14167 |
| 12 | 33279 |
| 13 | 111279 |
| 14 | 264191 |
| 15 | 882015 |
| 16 | 2105343 |
| 17 | 7023295 |
| 18 | 16809983 |
| 19 | 56055167 |
| 20 | 134348799 |
| 21 | 447916799 |
| 22 | 1074266111 |
| 23 | 3581236735 |
| 24 | 8592031743 |
| 25 | 28641504255 |
| 26 | 68727865343 |
| 27 | 229098477567 |
[0,0,4,9,34,71,245,543,1835,4223,14167,33279, 111279,264191,882015,2105343,7023295,16809983, 56055167,134348799,447916799,1074266111, 3581236735,8592031743,28641504255,68727865343, 229098477567] |