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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 6 |
| 3 | 24 |
| 4 | 72 |
| 5 | 220 |
| 6 | 652 |
| 7 | 1848 |
| 8 | 5160 |
| 9 | 14130 |
| 10 | 38102 |
| 11 | 101296 |
| 12 | 266328 |
| 13 | 692740 |
| 14 | 1785524 |
| 15 | 4563888 |
| 16 | 11577888 |
| 17 | 29170128 |
| 18 | 73032808 |
| 19 | 181793136 |
| 20 | 450100760 |
| 21 | 1108868820 |
| 22 | 2719167020 |
| 23 | 6639085968 |
| 24 | 16144137800 |
| 25 | 39107596850 |
| 26 | 94393612782 |
| 27 | 227062741160 |
| 28 | 544439640328 |
| 29 | 1301446217244 |
[0,2,6,24,72,220,652,1848,5160,14130,38102,101296, 266328,692740,1785524,4563888,11577888,29170128, 73032808,181793136,450100760,1108868820, 2719167020,6639085968,16144137800,39107596850, 94393612782,227062741160,544439640328, 1301446217244] |