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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 36 |
| 3 | 504 |
| 4 | 9576 |
| 5 | 229824 |
| 6 | 6664896 |
| 7 | 226606464 |
| 8 | 8837652096 |
| 9 | 388856692224 |
| 10 | 19053977918976 |
| 11 | 1028914807624704 |
| 12 | 60705973649857536 |
| 13 | 3885182313590882304 |
| 14 | 268077579637770878976 |
| 15 | 19837740893195045044224 |
| 16 | 1567181530562408558493696 |
| 17 | 131643248567242318913470464 |
[1,4,36,504,9576,229824,6664896,226606464, 8837652096,388856692224,19053977918976, 1028914807624704,60705973649857536, 3885182313590882304,268077579637770878976, 19837740893195045044224,1567181530562408558493696, 131643248567242318913470464] |