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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 4 |
| 2 | 24 |
| 3 | 60 |
| 4 | 480 |
| 5 | 2580 |
| 6 | 10200 |
| 7 | 59100 |
| 8 | 303600 |
| 9 | 1396500 |
| 10 | 7347000 |
| 11 | 37099500 |
| 12 | 180030000 |
| 13 | 916552500 |
| 14 | 4599165000 |
| 15 | 22749787500 |
| 16 | 114487050000 |
| 17 | 573173362500 |
| 18 | 2854795125000 |
| 19 | 14307190687500 |
| 20 | 71569168500000 |
| 21 | 357347616562500 |
[0,4,24,60,480,2580,10200,59100,303600,1396500, 7347000,37099500,180030000,916552500,4599165000, 22749787500,114487050000,573173362500, 2854795125000,14307190687500,71569168500000, 357347616562500] |