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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 2 |
| 3 | 9 |
| 4 | 44 |
| 5 | 325 |
| 6 | 2742 |
| 7 | 24794 |
| 8 | 250168 |
| 9 | 2796795 |
| 10 | 33842610 |
| 11 | 439337085 |
| 12 | 6100179780 |
| 13 | 90139379928 |
| 14 | 1409779442190 |
| 15 | 23242554452745 |
| 16 | 402652762232048 |
| 17 | 7308371248274949 |
| 18 | 138605556986785674 |
| 19 | 2740167375732394378 |
| 20 | 56350604098768558140 |
| 21 | 1203156656491936711635 |
[1,0,2,9,44,325,2742,24794,250168,2796795, 33842610,439337085,6100179780,90139379928, 1409779442190,23242554452745,402652762232048, 7308371248274949,138605556986785674, 2740167375732394378,56350604098768558140, 1203156656491936711635] |