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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 26 |
| 3 | 204 |
| 4 | 1899 |
| 5 | 21180 |
| 6 | 287568 |
| 7 | 4802716 |
| 8 | 99084889 |
| 9 | 2531896840 |
| 10 | 80346294380 |
| 11 | 3173108251044 |
| 12 | 156222183969181 |
| 13 | 9603287701405136 |
| 14 | 738066706464107408 |
| 15 | 71003673625149131020 |
| 16 | 8559188942710590217013 |
| 17 | 1294012524894298022238700 |
[1,4,26,204,1899,21180,287568,4802716,99084889, 2531896840,80346294380,3173108251044, 156222183969181,9603287701405136, 738066706464107408,71003673625149131020, 8559188942710590217013,1294012524894298022238700] |