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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 24 |
| 3 | 168 |
| 4 | 1286 |
| 5 | 10440 |
| 6 | 88112 |
| 7 | 764368 |
| 8 | 6766278 |
| 9 | 60828024 |
| 10 | 553529808 |
| 11 | 5086837680 |
| 12 | 47127896444 |
| 13 | 439608960656 |
| 14 | 4124536224864 |
| 15 | 38891699480992 |
| 16 | 368326082421446 |
| 17 | 3501654020899800 |
| 18 | 33403335855108368 |
| 19 | 319612386771594608 |
| 20 | 3066480362268978804 |
| 21 | 29493401582426082032 |
| 22 | 284301304326376855200 |
[1,4,24,168,1286,10440,88112,764368,6766278, 60828024,553529808,5086837680,47127896444, 439608960656,4124536224864,38891699480992, 368326082421446,3501654020899800, 33403335855108368,319612386771594608, 3066480362268978804,29493401582426082032, 284301304326376855200] |