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| n | a(n) |
|---|---|
| 2 | 1 |
| 3 | 4 |
| 4 | 20 |
| 5 | 138 |
| 6 | 1258 |
| 7 | 14476 |
| 8 | 202655 |
| 9 | 3354848 |
| 10 | 64246776 |
| 11 | 1398909332 |
| 12 | 34157026526 |
| 13 | 924757926320 |
| 14 | 27503093599024 |
| 15 | 891534666547216 |
| 16 | 31289986924954924 |
| 17 | 1182213869836721036 |
| 18 | 47846600590876178320 |
| 19 | 2065282617724684345208 |
[1,4,20,138,1258,14476,202655,3354848,64246776, 1398909332,34157026526,924757926320, 27503093599024,891534666547216,31289986924954924, 1182213869836721036,47846600590876178320, 2065282617724684345208] |