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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 40 |
| 3 | 196 |
| 4 | 844 |
| 5 | 3532 |
| 6 | 14784 |
| 7 | 60248 |
| 8 | 242792 |
| 9 | 977020 |
| 10 | 3920112 |
| 11 | 15702644 |
| 12 | 62855916 |
| 13 | 251527896 |
| 14 | 1006303768 |
| 15 | 4025613088 |
[1,4,40,196,844,3532,14784,60248,242792,977020, 3920112,15702644,62855916,251527896,1006303768, 4025613088] |