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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 18 |
| 4 | 128 |
| 5 | 1090 |
| 6 | 11232 |
| 7 | 134806 |
| 8 | 1849696 |
| 9 | 28550538 |
| 10 | 489656720 |
| 11 | 9237631150 |
| 12 | 190115847792 |
| 13 | 4238752713442 |
| 14 | 101775333547552 |
| 15 | 2618244556598310 |
| 16 | 71846664091504064 |
| 17 | 2094748778352174202 |
| 18 | 64666725024407102064 |
| 19 | 2107224874854168508126 |
| 20 | 72279858915240296971600 |
[1,4,18,128,1090,11232,134806,1849696,28550538, 489656720,9237631150,190115847792,4238752713442, 101775333547552,2618244556598310, 71846664091504064,2094748778352174202, 64666725024407102064,2107224874854168508126, 72279858915240296971600] |