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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 15 |
| 3 | 120 |
| 4 | 3060 |
| 5 | 278256 |
| 6 | 90858768 |
| 7 | 105637584000 |
| 8 | 436355999662176 |
| 9 | 6431591598617108352 |
| 10 | 340881559632021623909760 |
| 11 | 65533747894341651530074060800 |
| 12 | 46081376018330435634530315478453248 |
[1,4,15,120,3060,278256,90858768,105637584000, 436355999662176,6431591598617108352, 340881559632021623909760, 65533747894341651530074060800, 46081376018330435634530315478453248] |