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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 0 |
| 3 | 4 |
| 4 | 16 |
| 5 | 84 |
| 6 | 416 |
| 7 | 2084 |
| 8 | 10416 |
| 9 | 52084 |
| 10 | 260416 |
| 11 | 1302084 |
| 12 | 6510416 |
| 13 | 32552084 |
| 14 | 162760416 |
| 15 | 813802084 |
| 16 | 4069010416 |
| 17 | 20345052084 |
| 18 | 101725260416 |
| 19 | 508626302084 |
| 20 | 2543131510416 |
| 21 | 12715657552084 |
| 22 | 63578287760416 |
| 23 | 317891438802084 |
[1,0,4,16,84,416,2084,10416,52084,260416,1302084, 6510416,32552084,162760416,813802084,4069010416, 20345052084,101725260416,508626302084, 2543131510416,12715657552084,63578287760416, 317891438802084] |