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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 0 |
| 3 | 1 |
| 4 | 2 |
| 5 | 6 |
| 6 | 18 |
| 7 | 57 |
| 8 | 186 |
| 9 | 622 |
| 10 | 2120 |
| 11 | 7338 |
| 12 | 25724 |
| 13 | 91144 |
| 14 | 325878 |
| 15 | 1174281 |
| 16 | 4260282 |
| 17 | 15548694 |
| 18 | 57048048 |
| 19 | 210295326 |
| 20 | 778483932 |
| 21 | 2892818244 |
| 22 | 10786724388 |
| 23 | 40347919626 |
| 24 | 151355847012 |
| 25 | 569274150156 |
| 26 | 2146336125648 |
| 27 | 8110508473252 |
| 28 | 30711521221376 |
[0,1,0,1,2,6,18,57,186,622,2120,7338,25724,91144, 325878,1174281,4260282,15548694,57048048, 210295326,778483932,2892818244,10786724388, 40347919626,151355847012,569274150156, 2146336125648,8110508473252,30711521221376] |