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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 8 |
| 6 | 22 |
| 7 | 52 |
| 8 | 140 |
| 9 | 366 |
| 10 | 992 |
| 11 | 2684 |
| 12 | 7404 |
| 13 | 20440 |
| 14 | 56992 |
| 15 | 159440 |
| 16 | 448540 |
| 17 | 1266080 |
| 18 | 3587610 |
| 19 | 10195276 |
| 20 | 29057520 |
| 21 | 83018728 |
| 22 | 237737984 |
| 23 | 682196948 |
| 24 | 1961323740 |
| 25 | 5648590728 |
| 26 | 16294032160 |
| 27 | 47071589778 |
| 28 | 136171440600 |
[1,1,2,4,8,22,52,140,366,992,2684,7404,20440, 56992,159440,448540,1266080,3587610,10195276, 29057520,83018728,237737984,682196948,1961323740, 5648590728,16294032160,47071589778,136171440600] |