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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 8 |
| 2 | 52 |
| 3 | 320 |
| 4 | 1938 |
| 5 | 11704 |
| 6 | 70840 |
| 7 | 430560 |
| 8 | 2629575 |
| 9 | 16138848 |
| 10 | 99522896 |
| 11 | 616480384 |
| 12 | 3834669566 |
| 13 | 23944995480 |
| 14 | 150055305008 |
| 15 | 943448717120 |
| 16 | 5949850262895 |
| 17 | 37628321318280 |
| 18 | 238591135349700 |
| 19 | 1516500543586560 |
| 20 | 9660632784642840 |
| 21 | 61670325204822048 |
| 22 | 394451619337629792 |
[1,8,52,320,1938,11704,70840,430560,2629575, 16138848,99522896,616480384,3834669566, 23944995480,150055305008,943448717120, 5949850262895,37628321318280,238591135349700, 1516500543586560,9660632784642840, 61670325204822048,394451619337629792] |