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| n | a(n) |
|---|---|
| 0 | 4 |
| 1 | 16 |
| 2 | 84 |
| 3 | 496 |
| 4 | 3108 |
| 5 | 20176 |
| 6 | 134004 |
| 7 | 903856 |
| 8 | 6161988 |
| 9 | 42326416 |
| 10 | 292299924 |
| 11 | 2026332016 |
| 12 | 14085959268 |
| 13 | 98111307856 |
| 14 | 684331371444 |
| 15 | 4778093436976 |
| 16 | 33385561506948 |
| 17 | 233393582580496 |
| 18 | 1632228682596564 |
| 19 | 11417969833962736 |
[4,16,84,496,3108,20176,134004,903856,6161988, 42326416,292299924,2026332016,14085959268, 98111307856,684331371444,4778093436976, 33385561506948,233393582580496,1632228682596564, 11417969833962736] |