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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 52 |
| 5 | 140 |
| 6 | 356 |
| 7 | 880 |
| 8 | 2123 |
| 9 | 5016 |
| 10 | 11610 |
| 11 | 26400 |
| 12 | 59130 |
| 13 | 130476 |
| 14 | 284216 |
| 15 | 611592 |
| 16 | 1301344 |
| 17 | 2740194 |
| 18 | 5713930 |
| 19 | 11806144 |
| 20 | 24184908 |
| 21 | 49142504 |
| 22 | 99091244 |
| 23 | 198360536 |
| 24 | 394342884 |
| 25 | 778818658 |
| 26 | 1528531702 |
| 27 | 2982017956 |
| 28 | 5784365082 |
| 29 | 11158728448 |
| 30 | 21413292868 |
[1,2,6,20,52,140,356,880,2123,5016,11610,26400, 59130,130476,284216,611592,1301344,2740194, 5713930,11806144,24184908,49142504,99091244, 198360536,394342884,778818658,1528531702, 2982017956,5784365082,11158728448,21413292868] |