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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 6 |
| 4 | 15 |
| 5 | 21 |
| 6 | 74 |
| 7 | 211 |
| 8 | 914 |
| 9 | 4161 |
| 10 | 21216 |
| 11 | 115987 |
| 12 | 678800 |
| 13 | 4213611 |
| 14 | 27645078 |
| 15 | 190899418 |
| 16 | 1382961257 |
| 17 | 10480142165 |
| 18 | 82864882508 |
| 19 | 682076806179 |
| 20 | 5832742268693 |
| 21 | 51724158236232 |
| 22 | 474869816504724 |
| 23 | 4506715738447347 |
[1,4,6,15,21,74,211,914,4161,21216,115987,678800, 4213611,27645078,190899418,1382961257,10480142165, 82864882508,682076806179,5832742268693, 51724158236232,474869816504724,4506715738447347] |