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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 2 |
| 2 | 10 |
| 3 | 46 |
| 4 | 198 |
| 5 | 816 |
| 6 | 3264 |
| 7 | 12776 |
| 8 | 49192 |
| 9 | 186976 |
| 10 | 703328 |
| 11 | 2623072 |
| 12 | 9712864 |
| 13 | 35746816 |
| 14 | 130873088 |
| 15 | 476961920 |
| 16 | 1731331200 |
| 17 | 6262393344 |
| 18 | 22580421120 |
| 19 | 81188953600 |
| 20 | 291176175104 |
| 21 | 1041867493376 |
| 22 | 3720118018048 |
| 23 | 13257657264128 |
[0,2,10,46,198,816,3264,12776,49192,186976,703328, 2623072,9712864,35746816,130873088,476961920, 1731331200,6262393344,22580421120,81188953600, 291176175104,1041867493376,3720118018048, 13257657264128] |