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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 4 |
| 3 | 28 |
| 4 | 248 |
| 5 | 129140168 |
| 6 | 68630377364912 |
| 7 | 2088595827392656793085408064780643444068898148936888424953199350296 |
[0,4,28,248,129140168,68630377364912, 20885958273926567930854080647806434440688981489368\ 88424953199350296] |