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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 32 |
| 3 | 272 |
| 4 | 2400 |
| 5 | 21792 |
| 6 | 203008 |
| 7 | 1940224 |
| 8 | 19065344 |
| 9 | 193410560 |
| 10 | 2038078464 |
| 11 | 22490167296 |
| 12 | 262429339648 |
| 13 | 3271314362368 |
| 14 | 43955391856640 |
| 15 | 640254018879488 |
| 16 | 10121874150653952 |
| 17 | 173145693892509696 |
| 18 | 3186234896556752896 |
[1,4,32,272,2400,21792,203008,1940224,19065344, 193410560,2038078464,22490167296,262429339648, 3271314362368,43955391856640,640254018879488, 10121874150653952,173145693892509696, 3186234896556752896] |