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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 26 |
| 5 | 106 |
| 6 | 816 |
| 7 | 4292 |
| 8 | 90162 |
| 9 | 715138 |
| 10 | 10275886 |
| 11 | 87498566 |
| 12 | 1944309280 |
| 13 | 20988667064 |
| 14 | 380829128200 |
| 15 | 4301687654136 |
| 16 | 219999839271970 |
| 17 | 3375111608092354 |
| 18 | 90438559754079802 |
| 19 | 1341646116200287978 |
| 20 | 52342848299405537114 |
| 21 | 921821277222438350170 |
[1,1,2,4,26,106,816,4292,90162,715138,10275886, 87498566,1944309280,20988667064,380829128200, 4301687654136,219999839271970,3375111608092354, 90438559754079802,1341646116200287978, 52342848299405537114,921821277222438350170] |