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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 7 |
| 2 | 42 |
| 3 | 252 |
| 4 | 1512 |
| 5 | 9072 |
| 6 | 54411 |
| 7 | 326340 |
| 8 | 1957305 |
| 9 | 11739420 |
| 10 | 70410060 |
| 11 | 422301600 |
| 12 | 2532857460 |
| 13 | 15191434125 |
| 14 | 91114353750 |
| 15 | 546480693675 |
| 16 | 3277652052150 |
| 17 | 19658522431800 |
| 18 | 117906811965600 |
| 19 | 707175035973000 |
| 20 | 4241455800274875 |
[1,7,42,252,1512,9072,54411,326340,1957305, 11739420,70410060,422301600,2532857460, 15191434125,91114353750,546480693675, 3277652052150,19658522431800,117906811965600, 707175035973000,4241455800274875] |