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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 136 |
| 3 | 87904 |
| 4 | 1074100576 |
| 5 | 225184288253824 |
| 6 | 787061981348092400896 |
| 7 | 45273238870711805132010916864 |
| 8 | 42535296046210357883346895894694749696 |
| 9 | 649556283428320264374891976653586736162144180224 |
[1,4,136,87904,1074100576,225184288253824, 787061981348092400896, 45273238870711805132010916864, 42535296046210357883346895894694749696, 649556283428320264374891976653586736162144180224] |