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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 9 |
| 3 | 57 |
| 4 | 411 |
| 5 | 3181 |
| 6 | 25803 |
| 7 | 216486 |
| 8 | 1863139 |
| 9 | 16356925 |
| 10 | 145914573 |
| 11 | 1318844414 |
| 12 | 12051758083 |
| 13 | 111159508991 |
| 14 | 1033505202643 |
| 15 | 9675905948106 |
| 16 | 91140492185703 |
| 17 | 863107104436546 |
| 18 | 8212873185281571 |
| 19 | 78484928498979435 |
| 20 | 752928813642151089 |
[1,2,9,57,411,3181,25803,216486,1863139,16356925, 145914573,1318844414,12051758083,111159508991, 1033505202643,9675905948106,91140492185703, 863107104436546,8212873185281571, 78484928498979435,752928813642151089] |