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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 28 |
| 5 | 156 |
| 6 | 985 |
| 7 | 6575 |
| 8 | 46037 |
| 9 | 332729 |
| 10 | 2467215 |
| 11 | 18668476 |
| 12 | 143639875 |
| 13 | 1120736308 |
| 14 | 8848906376 |
| 15 | 70585065382 |
| 16 | 568063412434 |
| 17 | 4607556545105 |
| 18 | 37630962749979 |
| 19 | 309239715248494 |
| 20 | 2555320702164649 |
| 21 | 21220771891605441 |
[1,2,6,28,156,985,6575,46037,332729,2467215, 18668476,143639875,1120736308,8848906376, 70585065382,568063412434,4607556545105, 37630962749979,309239715248494,2555320702164649, 21220771891605441] |