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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 18 |
| 3 | 114 |
| 4 | 1030 |
| 5 | 13394 |
| 6 | 251962 |
| 7 | 6882102 |
| 8 | 273720022 |
| 9 | 15889775794 |
| 10 | 1349080450162 |
| 11 | 167821375177022 |
| 12 | 30636881867681934 |
| 13 | 8219778568738952282 |
| 14 | 3245381833135712948474 |
| 15 | 1887916233782601955737494 |
[1,4,18,114,1030,13394,251962,6882102,273720022, 15889775794,1349080450162,167821375177022, 30636881867681934,8219778568738952282, 3245381833135712948474,1887916233782601955737494] |