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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 18 |
| 4 | 64 |
| 5 | 220 |
| 6 | 782 |
| 7 | 2824 |
| 8 | 10328 |
| 9 | 38306 |
| 10 | 142388 |
| 11 | 533832 |
| 12 | 2011048 |
| 13 | 7609034 |
| 14 | 28938148 |
| 15 | 110276428 |
| 16 | 421716538 |
| 17 | 1616589438 |
| 18 | 6211475088 |
| 19 | 23925481704 |
| 20 | 92285891638 |
| 21 | 356644978016 |
| 22 | 1380284689858 |
| 23 | 5349558200316 |
| 24 | 20763135142878 |
| 25 | 80668088650424 |
| 26 | 313779804455788 |
| 27 | 1221721443853960 |
| 28 | 4761378554236090 |
[1,2,6,18,64,220,782,2824,10328,38306,142388, 533832,2011048,7609034,28938148,110276428, 421716538,1616589438,6211475088,23925481704, 92285891638,356644978016,1380284689858, 5349558200316,20763135142878,80668088650424, 313779804455788,1221721443853960,4761378554236090] |