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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 18 |
| 4 | 135 |
| 5 | 1013 |
| 6 | 8458 |
| 7 | 72257 |
| 8 | 628206 |
| 9 | 5556434 |
| 10 | 49815418 |
| 11 | 451476802 |
| 12 | 4128049326 |
| 13 | 38024311091 |
| 14 | 352446754137 |
| 15 | 3284400373590 |
| 16 | 30749731897370 |
| 17 | 289066731934716 |
| 18 | 2727216210298152 |
| 19 | 25812680778645432 |
| 20 | 245015325044029789 |
| 21 | 2331718909954888809 |
| 22 | 22242097596092999144 |
[0,2,18,135,1013,8458,72257,628206,5556434, 49815418,451476802,4128049326,38024311091, 352446754137,3284400373590,30749731897370, 289066731934716,2727216210298152, 25812680778645432,245015325044029789, 2331718909954888809,22242097596092999144] |