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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 2 |
| 3 | 12 |
| 4 | 68 |
| 5 | 360 |
| 6 | 1878 |
| 7 | 9716 |
| 8 | 50120 |
| 9 | 258192 |
| 10 | 1329322 |
| 11 | 6842396 |
| 12 | 35215884 |
| 13 | 181237368 |
| 14 | 932711806 |
| 15 | 4800019332 |
| 16 | 24702255760 |
| 17 | 127124540448 |
| 18 | 654216959826 |
| 19 | 3366774510892 |
| 20 | 17326314208468 |
| 21 | 89165799266952 |
| 22 | 458870789205926 |
| 23 | 2361470423992852 |
| 24 | 12152751175719000 |
[0,0,2,12,68,360,1878,9716,50120,258192,1329322, 6842396,35215884,181237368,932711806,4800019332, 24702255760,127124540448,654216959826, 3366774510892,17326314208468,89165799266952, 458870789205926,2361470423992852, 12152751175719000] |