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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 28 |
| 3 | 126 |
| 4 | 572 |
| 5 | 2692 |
| 6 | 13203 |
| 7 | 67542 |
| 8 | 360117 |
| 9 | 1999817 |
| 10 | 11541894 |
| 11 | 69098409 |
| 12 | 428183782 |
| 13 | 2742315847 |
| 14 | 18117294723 |
| 15 | 123222721469 |
| 16 | 861339730328 |
| 17 | 6179291890400 |
| 18 | 45431581077388 |
| 19 | 341893183760356 |
| 20 | 2630537501336631 |
[1,6,28,126,572,2692,13203,67542,360117,1999817, 11541894,69098409,428183782,2742315847, 18117294723,123222721469,861339730328, 6179291890400,45431581077388,341893183760356, 2630537501336631] |