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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 12 |
| 4 | 57 |
| 5 | 312 |
| 6 | 1950 |
| 7 | 13848 |
| 8 | 111069 |
| 9 | 998064 |
| 10 | 9957186 |
| 11 | 109305240 |
| 12 | 1309637274 |
| 13 | 17006109072 |
| 14 | 237888664572 |
| 15 | 3566114897520 |
| 16 | 57030565449765 |
| 17 | 969154436550240 |
| 18 | 17439499379433690 |
| 19 | 331268545604793240 |
| 20 | 6624013560942038670 |
| 21 | 139080391965533653200 |
| 22 | 3059323407592802838180 |
| 23 | 70355685298375014175440 |
[1,1,3,12,57,312,1950,13848,111069,998064,9957186, 109305240,1309637274,17006109072,237888664572, 3566114897520,57030565449765,969154436550240, 17439499379433690,331268545604793240, 6624013560942038670,139080391965533653200, 3059323407592802838180,70355685298375014175440] |