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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 73 |
| 5 | 285 |
| 6 | 1161 |
| 7 | 4862 |
| 8 | 20771 |
| 9 | 90353 |
| 10 | 399091 |
| 11 | 1784543 |
| 12 | 8055832 |
| 13 | 36659569 |
| 14 | 168035062 |
| 15 | 775172993 |
| 16 | 3595679620 |
| 17 | 16757243082 |
| 18 | 78421752518 |
| 19 | 368401565131 |
| 20 | 1736597767880 |
| 21 | 8211214974202 |
| 22 | 38932098919426 |
| 23 | 185053094175915 |
| 24 | 881632597237259 |
| 25 | 4209197016287761 |
| 26 | 20135026894225442 |
| 27 | 96489130448473609 |
[1,2,6,20,73,285,1161,4862,20771,90353,399091, 1784543,8055832,36659569,168035062,775172993, 3595679620,16757243082,78421752518,368401565131, 1736597767880,8211214974202,38932098919426, 185053094175915,881632597237259,4209197016287761, 20135026894225442,96489130448473609] |