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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 9 |
| 4 | 19 |
| 5 | 100 |
| 6 | 279 |
| 7 | 1189 |
| 8 | 3781 |
| 9 | 14661 |
| 10 | 49600 |
| 11 | 184141 |
| 12 | 641421 |
| 13 | 2333629 |
| 14 | 8240959 |
| 15 | 29700900 |
| 16 | 105561739 |
| 17 | 378777169 |
| 18 | 1350292761 |
| 19 | 4835148121 |
| 20 | 17260998400 |
| 21 | 61748847081 |
| 22 | 220582688041 |
| 23 | 788748162049 |
| 24 | 2818480203099 |
| 25 | 10076047502500 |
[0,1,1,9,19,100,279,1189,3781,14661,49600,184141, 641421,2333629,8240959,29700900,105561739, 378777169,1350292761,4835148121,17260998400, 61748847081,220582688041,788748162049, 2818480203099,10076047502500] |