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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 48 |
| 3 | 640 |
| 4 | 8960 |
| 5 | 129024 |
| 6 | 1892352 |
| 7 | 28114944 |
| 8 | 421724160 |
| 9 | 6372720640 |
| 10 | 96865353728 |
| 11 | 1479398129664 |
| 12 | 22684104654848 |
| 13 | 348986225459200 |
| 14 | 5384358907084800 |
| 15 | 83278084429578240 |
| 16 | 1290810308658462720 |
| 17 | 20045524793284362240 |
| 18 | 311819274562201190400 |
| 19 | 4857816066863765913600 |
[1,4,48,640,8960,129024,1892352,28114944, 421724160,6372720640,96865353728,1479398129664, 22684104654848,348986225459200,5384358907084800, 83278084429578240,1290810308658462720, 20045524793284362240,311819274562201190400, 4857816066863765913600] |