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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 4 |
| 4 | 24 |
| 5 | 72 |
| 6 | 312 |
| 7 | 1088 |
| 8 | 4288 |
| 9 | 15744 |
| 10 | 60192 |
| 11 | 224832 |
| 12 | 851072 |
| 13 | 3197056 |
| 14 | 12062592 |
| 15 | 45398016 |
| 16 | 171104256 |
| 17 | 644354048 |
| 18 | 2427699712 |
| 19 | 9144222720 |
| 20 | 34448209920 |
| 21 | 129761986560 |
| 22 | 488821962752 |
| 23 | 1841370087424 |
| 24 | 6936475090944 |
| 25 | 26129575084032 |
[0,2,4,24,72,312,1088,4288,15744,60192,224832, 851072,3197056,12062592,45398016,171104256, 644354048,2427699712,9144222720,34448209920, 129761986560,488821962752,1841370087424, 6936475090944,26129575084032] |